Also would like to support Dugtrio A --> A+ because it's literally the face of stall. Dugtrio is literally a requirement on stall, and recent tournament play has proven this. It's the face of the playstyle, moreso than Mega Sableye or Chansey. But Dugtrio also finds itself being very effective on offense for the same reason. It pairs well with so many sweepers (espeially Fightinium-Z SG Magearna). It's one of the very few Pokemon that finds itself being an amazing choice for every team, and I think this is the reason it warrants the rank up.
You're right in the fact that Dugtrio is invaluable to stall, but it's not an amazing choice for every team like you stated. In fact, it's very situational and mu reliant. It does aid offense and certain mons like Zard-Y & Volc very well, but is not a complete necessity either. All these points were stated in Gary's post last update when it rose to A and nothing really has changed since then to make it rise to A+.
Nevertheless, I think Dugtrio is a better fit in A than A+ because when I look at A+, I see mons that have an impact on the battle 8/9 times out of 10. Someone from the ranking team made a really good post about this before but I couldn't find it unfortunately. Both Greninja forms, Celesteela, Heatran, Zygarde, and so on fit this description - their combination of typing + movepool makes them annoying for most teams to face and they can contribute a lot to a variety of different teams.
Dugtrio, on the other hand, has a hard time succeeding vs more common defensive cores - think Tangrowth/Mew, Lando-T, Celesteela, etc. I think Duggy is definitely more comparable to the impact that mons in A have than A+ (Pinsir, Koko, Ferro, Keldeo, etc). It also isn't very hard to revenge kill with priority, scarf users, faster mons, or mons it just can't touch in general. For this reason, I think
Duggy is fine in A.
I have hard time believing that
Dragalge is unranked. This mon does really well in this meta, deserving C+ or even higher.
Since metagross ban everything went well for this mon. Gengar, nihilego, and other posion types went down in usage, leaving much room for Tspikes support. Volcarona is not used as much so you don't have to be afraid about Z-Psychic. Most spammed mons like Zaptos, Koko, ZardY, Bulu, Keldeo are beaten by it. Rain is more popular so another thing able to come on specs hydro is needed. Dragalge is suprisingly good right now.
Tspikes are godlike right now. Well played can poison Mew, Fini, Tangrowth and bring them down to the point the cannot wall anything (tangrowth takes almost from
scarf keldeo if rocks and tspikes are up). Since half of meta has bad matchup against dragalge it is to lay them down.
And now some replays showing how much support gives and how good dragalge is:
http://replay.pokemonshowdown.com/gen7ou-598473284
Thanks to Tspikes Heracross is able to murder half of enemy's team.
http://replay.pokemonshowdown.com/gen7ou-598468323
After ground types are dead, dragalge almost deals with rest of rain team.
http://replay.pokemonshowdown.com/gen7ou-598453890
Same deal. Excadrill dies, Tyranitar dies and suddenly nothing can deal damage to Dragalge.
This mon is way too solid to be unranked.
Although I wouldn't oppose a Dragalge rise (I honestly haven't even used the thing lol), I don't think it's all too viable in the current meta, especially not for C+. I'm not sure what spread you're using so my apologies if I state something wrong.
For starters, it can't switch in to Lando, Zygarde, Garchomp, or Latios, can't touch Magearna, Celesteela, Heatran, and Ferro, gets trapped by Duggy, almost dies to +2 Grassium Bulu (depends on the spread but Rockium destroys it), loses to Volc if it QD's on your switch (unless no HP Ground/Psychic, but this definitely means Duggy support), loses vs Mawile, struggles vs Tyranitar as it can DD on it, and even stuff that it's supposed to beat like Mew/Tangrowth still have a chance to beat it if they don't switch in on a layer of Tspikes (if you switch in to Tangrowth, you risk EQ or even Knock), and Chansey is everywhere.
Of course, this stuff is all on paper and some even depend on your last move (Focus Blast/HP Fire/Scald), but it shows that 1) it's not very easy to get Dragalge in and 2) it gets forced out a lot by popular mons. Even stuff like rain has Specs Pelipper, Swampert, and Ferro, and one wrong prediction vs Kingdra can suck.
Lastly, I think the replays are a bit lacking; they don't really show "how good" Dragalge is in the sense that: Not sure why your opponent went for Pursuit in the second one (Knock was much better even if he expected Suicune, as it 2hkos) and he could've just killed Dragalge, and in the last one your opponent sacks Excadrill for some reason and then missed the last Fire Blast (altho tbh, he should've just sacked Keldeo).
Overall, I think that if I wanted to use Tspikes, I would just opt to use Toxapex, but I do get that Dragalge brings some offensive presence with it too. Just wanted to give my two cents on it amd why the majority of the meta is unkind to it and why the replays don't merit it a C+ ranking.
Some other points which I sadly can't elaborate on more atm:
Chansey should rise. It's an amazing answer to all the special attackers running around and provides offense with defensive relief.
Mega Venusaur should also rise. The reasons were stated in previous posts, but its overall bulk makes it annoying for many unprepared teams to break through.
Indifferent to a Mew rise.
Disagree with Zapdos to A, but I don't use it enough to chime in on it.
A couple of noms I'll write about later but will mention here to remind myself:
Gengar A- ---> A
Tapu Fini B+ ---> A-