My biggest problem with Jax is he can fill every real important role in a team battle.
He can dodge tank.
He can incapacitate.
He can be a dps carry.
He can chase painfully effective.
He can tower dive with little fear.
He can push and farm well with aoe.
And he can do them as well, if not better, than heroes that can only do 1 or 2 of those.
When jax can fill the necessary roles of most of a team, that's when I would draw the line.
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