Well, there are quite some stuff I want to say / am confused about, so the post may be long.
First, I just build a kinda different sun team than most of them. While some of the stuff may be a little unorthodox, so most people aren't that prepared, but I'm pretty sure they deserve a rank.
Roserade is the star of my team, and is in my opinion the best non-fire Sun sweeper in the tier right now. While its sheer power isn't as destructive as Heatran's, it has a very powerful SolarBeam and gets Weather Ball, which is really good coverage. Something else which differentiates it from Heatran is that it can easily run Life Orb. Heatran usually wants Eruption (or at least that's the set it's known for to) to sweep and wallbreak everything at the same time, but for this it needs Specs if it doesn't want to wear itself down. When it does run Fire Blast + Life Orb, it's weaker than Roserade besides Fire Blast STAB (which is admittedly extremely powerful), however missing is annoying. Of course, it also brings a different typing to the table. Sludge Bomb is also a nice move for bulky fairies.
Something else that makes it good is the ability to get past most any one counter, with Sleep Powder. I'm pretty sure you all know how good this move is, so I won't go out of my way explaining it, but it basically makes one Pokemon on the other team useless (when it hits .-.). Basically letting it cripple and possibly get past a counter.
The biggest downside for it is its weakness to Gale Wings, which you should really attempt to patch up if you're building with it. A few other priority moves as ExtremeSpeed (especially Refrigerate) work, but it also resists quite some (Mach Punch, Aqua Jet), while Sleep Powder can neuter Sucker Punch. Otherwise few can actually handle it well with Chlorophyll and a little residual damage. Of course, sun running out is terrible for it, but seven turns is more than enough for a sweep, and forces the opponent to predict really well.
Because of these points, I think it should be
C+. It's quite powerful, and hard to stop if it gets going, but it needs quite some support and a free switch-in. (Saccing, Double Switching, Slow VoltTurn, and bulky Waters)
Delphox is an underrated Pokemon. While I won't say it's great, it works well on a sun team as a wallbreaker and is
definitely better than Houndoom. With Choice Specs and Solar Power, its power is shocking, as Fire Blast boosted by sun, specs and STAB is really powerful. I'll start with some calcs to compare its power.
252 SpA Solar Power Mega Houndoom Fire Blast vs. 252 HP / 0 SpD Mew in Sun: 427-504 (105.6 - 124.7%) -- guaranteed OHKO
252 SpA Choice Specs Solar Power Delphox Fire Blast vs. 252 HP / 0 SpD Mew in Sun: 553-652 (136.8 - 161.3%) -- guaranteed OHKO
252+ SpA Choice Specs Heatran Eruption (150 BP) vs. 252 HP / 0 SpD Mew in Sun: 604-712 (149.5 - 176.2%) -- guaranteed OHKO
252+ SpA Choice Specs Solar Power Delphox Fire Blast vs. 252 HP / 0 SpD Mew in Sun: 607-715 (150.2 - 176.9%) -- guaranteed OHKO
As you can see, it's stronger than Mega-Houndoom, a Pokemon which is apparently in C-rank. I think Delphox pretty much outclassed Mega-Houndoom unless you want a standalone wallbreaker, which is bad anyway, but I'll explain that later.
First, on sun teams, Mega-Houndoom takes the Mega slot, which is more valuable than you may imagine since Mega's like Mega Diancie are great for Sun, and I imagine others being good too, like Mega Altaria. Also because of this Mega-Slot, it can't use an item, which actually causes it to be weaker than Specs Delphox. While its speed allows it to outspeed a bit more than Delphox, both are quite fast. Mega-Houndoom also has the disadvantage of starting at 90 base Speed, which is actually slower than Delphox and outslows many critical Pokemon. The competition of Dark vs. Psychic STAB is equal in my opinion, as the things they hit SE don't really matter, and it's just about hitting some stuff that you can't hit with your Fire-STAB. Both need Sun-support to shine as well. So if I want a Solar Power Wallbreaker, I'd choose Delphox, because it's more powerful. It also has Switcheroo to annoy stall.
Heatran is possible to be used, but gets worse quickly as it gets worn down.
So if you guys feel Mega-Houndoom's ranking was right, I want this at
C, because it needs quite some support, but is really powerful on the right teams. It may be a niche option but can easily shine when used well.
Additionally Mega-Houndoom should go to
D. There are many other wallbreakers in this metagame and Mega-Houndoom only gets one chance to wallbreak if it isn't on a sun team, since if it's forced out after it mega evolved, it can't get the sun back anymore and is pretty mediocre. It's also quite frail and hard to mega evolve. So it's generally better to use something else.
Diancie-Mega is underrated. It's Mega is not even on the viability rankings, even though it's great! I actually think it's one of the better megas in the tier. To start, like most mega's, it's a great abuser of Illusion. With its unique set of resistances and powerful attacks, you can easily fool Pokemon like Goodra and various birds in thinking they can easily stay in and KO you, when they do pitiful damage when you One- or Two-Hit-KO them with its base 160 offenses. Mega-evolving isn't even an issue, as while you're slow you can force a lot out, or just fool them in thinking tha tyou're something different, so you can easily get to your mega-form. It can also use Download to boost either offense as it can abuse both, but I haven't used that set.
Besides its powerful attacks (even mixed!), it gets two moves that help it in sweeping: Rock Polish and Calm Mind. Both are viable and various teams can abuse them. Rock Polish allows you to outspeed pretty much everything in the metagame, even though you outsped most things already, while Calm Mind allows you to boost on certain things that can't hurt you, or switch out so your Special Attacks and bulk get boosted. Rock Polish can easily sweep offensive teams when Bullet Punch and Aqua Jet users are removed, (and be careful around Gale Wings, while you resist it, they still do a lot, so make sure you don't get weakened too much) and wear certain things down. Against Stall, it's a pain as well since Calm Mind and Magic Guard make it so that it can stallbreak a lot of Pokemon. Illusion doesn't help either!
After considering its mixed and powerful attacking, is not even frail, boosting and the fact that it can check a lot of Pokemon I think this should be
A- or
A.
Virizion surprised me. I initially added it to my team as I needed a fast Fighting type, and I wasn't too happy with it, but it really did way better than I expected. I used Magic Bounce to set up on many stallier threats, as a combination of its bulk and Magic Bounce gave issues to a lot of Pokemon. It's true that it isn't that good against offense, but balance and stallier builds can truely have a problem with it. The combination of Swords Dance and Synthesis, in addition to its stats makes it so that it can set up moderately easy, and beat Pokemon as Goodra, Ferrothorn, Suicune, Vaporeon, non-SD Scizor, Tyranitar and more! While it indeed struggles against offense, since they'll often have Pokemon that are fasted and can KO it, or Pokemon that it can't KO and pressure it. Against stall you need a way of removing or weakening Skarmory and Doublade, since they're the most annoying things to it. It also has issues with a few Unaware users, but it can handle Suicune as long as you don't get burned turn one. Cresselia is mostly annoying. Otherwise it can handle most things. Luckily you have teammates! That's pretty much all I can say about it, but it is really surprising and can tank most special hits (even non-STAB SE ones) and most weaker physical hits. Considering this, I'd move it to
C- or
D, since I agree its fairly niche and needs to be on the right teams that both need its capabilities, typing and can support it well.
Skarmory should probably be moved down. It's not as good anymore and is easily pressured. It can sweep lategame yes, but it's not nearly as good anymore. If I wanted to check Gale Wings I wouldn't use its own Gale WIngs set either, and Honchkrow can just get past it.
Other things that confuse me but I didn't use, but want to see some discussion about:
Heracross in A.
Swampert in A-.
Finally, there seems to be rank inflation. There are tons of Pokemon in the higher A ranks and I'm sure some can be moved down. I'm not sure which, but maybe you guys do, so maybe discuss that! There are also way fewer Pokemon in B and even less in C which further exemplifies my point. While most Pokemon in A / A+ are good, it does seem like some could be A just fine, as we need to draw the limit somewhere, as currently it seems like the "I think this Pokemon can be good and I like it on my team, so it hsould probably be a high rank".
That's it, for now~