The time to kill in this fighting game is much too fast, even faster when everyone neglects defense gear for offensive gear. Everyone can vaguely recall getting ganked and dying in 2 seconds, but if you had more HP it would feel like an actual fight. Instead of dying in 2 seconds you die in 10 seconds instead or longer since you would pop revenge more. For now nubs die too quickly to learn the game and it doesn't seem very fun to play to them (I assume).

Most other iconic fighting games (smash bros, mortal combat, tekken, , soul caliber) has much higher time to kill and is generally deemed much more fun because of it.

More HP would mean more chances for mistakes and longer fights.

The difference between a heavy and an assassin's HP pool will be more pronounced. Catapult shouldn't one shot kill all the time anymore. Getting Shogi hugged when his buddies are around won't be instant death.

Even if you won't do this for the main game you should easily be able to test it in an event where everyone gets a buff that doubles or increases their HP by X amount.