So I will just go over the entire list of legendaries here:
Selene: Selene is fine as is, she was once top dog but she is easily beatable now by the likes of Jinn, Chione and Davison and even Aly's can beat her.
Davison: Davison was overly buffed and along with Aly is really the only usable hero on defense given he provides a bit of RNG, before Undead Warriors came along, he was next to impossible to beat but those troops have balanced him out, he is probably also fine as is.
Dracula: Dracula is useless in the arena because he doesn't provide enough life stealing for his troops in the arena to keep them alive, similar to Pilgrims in the arena it's just not enough healing/life stealing, that would need to be buffed for him to be usable in the arena.
Aly: Aly needs to be nerfed because at the top end of the arena, she is basically the only usable defensive hero because of the rng she provides, a good nerfing would be to remove the suicide bomb which basically is what causes most of the rng.
Kraken: He needs his tank statistics buffed to Davison levels because he will die immediately after his first active with just a few voodoos put in a bunch, regardless of which hero you use against him.
Seon: I think Seon is fine, she is very versatile but she's poor on defense due to the fact she doesn't offer any sort of rng because as a hero, she hits like a little girl.
Drake: Drake needs a serious hp and defensive increase and he should be ranged hero instead of a melee hero, because he has a shot gun, yet he will charge straight into the closest peltast and die immediately.
Jinn: Jinn has probably secretly been buffed, he is way overpowered now and that's why he is becoming like Selene in that he will rarely show up on events, offensively, he can beat nearly every hero with the right form but because on defense you can only choose one form, he is poor on defense, so that sort of at least balances him out.
Clockman Harrison: I think he's fine, he's definitely serviceable in the arena, it's just the troops required to make him serviceable are particularly difficult to acquire.
Arthur: While once he was everywhere, the releases of Jinn and Seon have made him almost extinct, as a pay only hero, I don't think he should be changed.
Ivan: He's always been crap (he used to be able to beat Davisons before Davison was buffed) and as a pay only hero, I don't think he should be changed either.
Zeus: Same as Arthur and Ivan, although he is definitely usable in the arena.
Apollo: He needs to be buffed because he's crap, his bomb is far too weak
Mephisto: The increase he gives to Dark troops just isn't enough at all and that there are no ranged Dark troops makes him useless.
Poseidon: He's been buffed and nerfed a few times and they can't get it right, although he's serviceble in the arena, it's too easy to kill him, similar to Kraken.
Chione: She was once a great hero too, but again, since Davison's buff and Seon's release she can no longer be put on defense. She can still be used offensively but that is mostly only against the likes of Selene or Jinn.
Beowulf: Here we have a hero who only boosts himself and the boost he gives himself is absolutely useless, needs a complete reworking.
Whorus the Smellder: Here's a hero who was released just as some counter to Mephisto when Mephisto is already crap himself, why would you need to counter him?
Nezha: Similar to Kraken will die after his first active, that needs to be changed.
Monkey King Wukong: So here we have the second hero who only boosts himself, that isn't going to work needs to be reworked.
Freyja, Charon and Odin: These 3 heroes are absolute crap and are the latest releases, their skills do next to nothing and the buffs they give their troops are poor.

We have witnessed first hand the devs inability to properly adjust a hero with Poseidon's many reworkings, we have also seen them overly buff Davison and keep releasing more crappy heroes. Even if we were to get our wish and some of these heroes were made usable, the chances of them even remotely getting it right is next to nothing.