I agree that ease of use is much more based on how easy a character’s neutral game and hit confirms are. Combos don’t matter as much not only because they can be practiced in training mode, but also because even if a character has more difficult or advanced combos available, they generally also have very easy, basic combos which still deal reliable damage. For example, Dr. Strange’s impact palm loops are quite difficult, but he can also just do ABC ABC super and get nearly 500k with basically 0 chance of ever dropping it. There are a few exceptions where characters legitimately cannot get even halfway decent damage without doing more advanced stuff, but they are very few and far between.
Easy to use characters have a strong, simple and easy-to-execute gameplan from anywhere on the screen. The more regions of the screen they have this kind of gameplan from, the easier to use they are. This is why Vergil and Wesker are so easy; with literally only 1-2 moves, they are able to remain a threat from anywhere at any time. My list would be:
Capcom:
Easy: Akuma, Nemesis, Spencer, Dante, Vergil, Wesker
Medium: Amaterasu, Frank West, Trish, Zero, Haggar, Ryu
Hard: C. Viper, Felicia, Firebrand, Tron, V. Joe, Morrigan
V. Hard: Chris, Chun-Li, Hsien-Ko, P. Wright, Jill
Unsure: Arthur, Strider (both of these I’m unsure on because of their potential for anchor XF 3 derp, in anchor position I would put them at medium, but on point I would prolly have Arthur as V. Hard and Strider as Hard)
Mahvel:
Easy: Capt. America, Hawkeye, Hulk, Nova, Taskmaster, Wolverine
Medium: Deadpool, Dr. Doom, Dormammu, Ghost Rider, Magneto, Super-Skrull
Hard: Dr. Strange, Iron Fist, Sentinel, Storm, Thor, X-23, Spider-Man
V. Hard: Iron Man, MODOK, Rocket Raccoon, She-Hulk, Shuma-Gorath
Unsure: Phoenix (I’m torn on her for obvious reasons, people can just stick her in 3rd and derp it out with XF3 DP whenever they get 5 bars, and win plenty of matches that way while having no clue how to play regular Phoenix, or often even XF-less DP)