Where would Guillotine rank if she were part of another class?
We see a lot of posts talking about where champs rank within their own class, but mystics is in a class by itself. The top 6 mystics are probably DV, SW, Magik, GR, Mordo, and Dormammu. I'd personally probably put Red Hood at 7 and Guillotine at 8. It's not a precise science, but it's hard to argue she is a top 5 mystic champion.
Would she crack into the top 5 in any of the other classes?
Mutant - Wolverine, X-23, Iceman, Rogue, and AA clearly outclass her
Science - The two Spiderman are beasts defensively, but if we look just at attack she probably slips in around #5 with YJ following both CAs, Hulk, and Quake
Tech - SL and Stark SM are light years ahead, but she might compete for the fifth spot behind them, Ultron and Vision (assuming we count them as 1)
Cosmic - Hyperion, Drax, Medusa, Angela and Thor generate a lot of damage. She is more versatile, but I don't think she cracks into this top 5.
Skill - GP is best in class hands down, but the rest is open to debate, because many of these (like XB) require some skill to learn how to use.