Characters with bigger hitbox should have more health

They differ quite a bit.

I think HP can solve these things, but they would have to be extremely careful about it and mind damage thresholds and things like that.

Also, people like to exaggerate numbers because they are inexperienced with balancing asymmetrical games.

I've seen people advocating for Gibraltar to have 175 hp and for armor to work better for him (ie blue armor giving 100 hp etc). That's ridiculous.

A logical starting point would be around 110hp, for example. It doesn't break the melee threshold (still 4 punches needed), which is good. But it does break certain thresholds, which is also good. For example, a full fitted wingman doesn't kill that character with two headshots (202dmg). This is just one example of how these things should be approached. The game is very much a fps at its core, so any ow-like approach is very dangerous to have.

Lastly, I'll give an example from SFV, not the same genre in the slightest lol, but just to emphasize the notion of how how iffy HP balancing can be. In SF, average health is about 1000. So, anywhere between 900 and 1100 or so.

Now, if you have a 1000 hp character and nerf his health to 950, that's considered a significant nerf. If you take a 900hp character and give him 25 additional heatlh (that's 25 on a 900), that's also a fairly decent buff. If you buff a 900 hp character to 975 health, that's almost never done as it's considered kinda ridiculous thing to do in a single step.

And all that is true without any thresholds - ie, there aren't damage thresholds which make a 900hp character killable to certain established sequences and a character with 950hp jumps out of that range. It's just a raw percentage addition.

So, it's not like OW in that regard (ie, tracer has 150hp and she can't have 140 because that's one shot for mccree etc - there aren't these notions in sf).

So, I think overall, hp balancing might do the trick, but one has to be extremely careful about it.