I disagree, Renathal indeed dismantles agro decks based solely on quick face damage like DH or Quest Hunter, having more health doesn't guarantees you're going to have removal. Yes, it makes it statistically more probable, but it doesn't. Efficient board generation decks will still be viable and will probably still kick Renathal deck asses. I do agree that agro disappearing is totally bad for the game. Agro needs to be there. I like all kind of decks, I played agro, combo, midrange, control and even meme decks with no sense lol. All serve a purpose.
What needs to be done is actually increase the ceiling of the game a little bit. Lets be honest, you can't play around an insane amount of direct damage unless you have extreme heal or dumb armor generation (which was the current strategy). That play style is toxic, we have seen it before a lot. Having more life from start is not equal to having an entire deck for generating armor and healing. So, a play style with not so many counters what finally does is lowering the ceiling of the game. How many times have you lost against a face hunter or DH that you visually saw counting poorly, making trades when he clearly didn't needed to do it so? It's something that happens. And it's to blame the abusive amount of face damage we have...
TLDR, IMO Renathal is the clean solution for the problem of too much face damage.
I agree that decks which pump ridiculous amounts of damage to the face are problematic. Mine Rogue, Curselock, Garrote Rogue, various Mages, etc. You're right that lifegain is the only way to mitigate those strategies. But I don't really consider decks like that "aggro". If a deck can deal 20+ damage to you in a single turn from hand, I would consider it a combo. Popping off with a million spells and hero powering with Quest Hunter is essentially a linear combo, Smite + Sunken Vessel is a two-card combo, Brann + 2 Curse Battlecries is a 3 card combo, etc.
Aggro, to me, plays on board and hits you with dudes until you die. Traditional Face Hunter, most Demon Hunters, Pirate Warrior, Aggro Shaman decks, etc. And when it takes 3 more turns or so to put your opponent to 30 Health, that presents an issue for those decks. Anecdotally, I finally started playing Demon Hunter now that I have a skin that isn't an angry guy. I've got a really fun Token Demon Hunter deck in Wild that I play casually because I like the strategy. The extra turns it takes to kill my opponent gives them enough time to put me on the back foot, wipe my board, and keep me from getting through fairly consistently. Now I know this isn't the best version of the deck, and I'm not the best pilot, but that's what I've experienced.
I guess Aggro can also be like Questline Shaman, since it'll play kinda like Mono Red Burn in MTG. Tossing burn spells face and attacking with dinky creatures is aggro. But 10 health is a lot to a burn/aggro player.
I think it's easy for Control Players to believe that 10 Health isn't that much because the style of game they play is different from Aggro. Every Control-Lock ever would happily trade 10 Health for 5 cards. But the gap is huge for Aggro to clear early. Turns 1 through 4 they just don't have access to that kind of over-the-top damage. And after that point, if your opponent isn't already on the back foot, it's so easy to lose all your tempo and the game.
TLDR: yeah decks that deal 20+ damage from hand are toxic and difficult to interact with. but i think a better solution is preventing those strategies from being dominant. Not making cards that enable those strategies to flourish. Giving all Control decks more starting health seems inelegant, and dances around the actual problem of designing cards that make toxic strategies work. Also, even if this is the best response, it's still an expensive one.