Sylveon is pretty overrated in these threads, when it's just not great in practice. Sure it nukes w/specs, but a bunch of teams carry a good fairy resist, which walls it without the specific HP coverage. It's also very prediction reliant, which can be a complete momentum killer if you Hyper Voice into a resist. It's just so slow and without defensive investment, is pretty frail and easy to take down, and things like Jirachi rising in usage doesn't help it at all as it gives it issues as it needs Shadow Ball to hit Jirachi, and has to lose out on coverage or Baton Pass, A- is completely overselling it and if it does rise, it shouldn't go any further than B+.
However, I think Victini is really interesting in this meta, as it's one of the best offensive checks to Mega Metagross and most fire types, outside of Earth Power Heatran, it can be an effective Wallbreaker with CB due to the sheer power of Banded V-Creates, or it can opt for a Scarf revenge killer set, which lets it deal with fast threats like MMeta, Mega Lopunny, Scarf Lando-T, Keldeo, Gengar, Gyarados, Mega Gallade, Tornadus-T, Mega Beedrill and more. Its got good coverage through moves like Bolt Strike, Glaciate (it's so good for picking off weakened 4x resists and a speed drop on something like Lando-T pressures it to switch so much), Grass Knot (which is all it really needs + STAB). It does have it's flaws such as having an awful defensive typing in general, being SR weak and being extremely weak to pursuit trapping. And even then, it can opt for a SubPup set which lets it break bulky waters and Heatran + TTar who all check / counter it. It's fairly unpredictable to a degree as you can't tell if it's running Adamant CB Wallbreaker, Scarf Revenge killer or SubPuP. I think it should be B+ as it's just not on the level of Conkeldurr or Mega Sharpedo