I can speak from personal experience about some of these heroes, since I only play with 4*:
cChao is great in Trials quests and for completing Legendary challenge events and for stealing the mana of tough, but slow-charging bosses like the ones in the Tavern of Legends or Costume chamber last stages. He is OK in raids and tournaments as well. I doubt that he will be great if you want to compete in challenge events though.
Griffin has better stats than cChao, and is generally probably the best pure 4* yellow sniper there is, so I’d say he should take priority over cChao if we’re talking about main target being 4* raid tournaments. I don’t have him though, just speaking theoretically here.
Chesire Cat I see being constantly used vs 14* yellow titans, so I guess there are no better purple pure def down heroes.
Cyprian I used a lot to develop myself early game, but now I stripped him of his emblems and he’s taking the bench now for quite a while. So my guess is he’s a decent early game, not much use late-game.
Hu Tao is great in very fast events as others already mentioned, but also on harder map stages where his blind keeps everyone in check and serves as a massive heal.
From the blue heroes I could see Sapphire being okay-ish. Maxing her depends on what other blue 4* you already have.
From the reds I constantly use Sumle, cKelile and cScarlett (the latter only for costume bonuses). They are all ok, but cScarlett is the best amongst them. Sadly my Sumle misses a lot and in the most important cases which will probably make me reconsider his usefulness and strip him of his 19 nodes of emblems. But for very fast events he’s still great. I can see Mack being okay-ish as a tank in 4* raid tournaments where blues are banned.
From green, cKashhrek sees a lot of praise. I have him but really am not that impressed by him. Yet he’s decent and you can safely max him. I concur that Peters and Tettukh should be maxed - for example they can help versus Blue rare high* titan where you can’t bring Mikki along, but they can also have other uses. cSkittles is probably a good option vs the blue Mythic titan where the quantity of high-tile green hitters is important for achieving max score, and also in very fast tournaments.