Honestly, I think tryndamere is balanced as he is for TT.
Yes he does deal heavy DPS
Yes he is very hard to kill
But so what?
Every champion in the league is counterable
You don't even need to counter him at champion select. Just got to build the right items and conserve your CC.
I don't even remember the last time I lost a game to tryndamere.
Lee Sin is a lot harder to fight than tryndamere, but that's about it. He may be harder, but he's not impossible. If you are fighting a capable lee sin, and you are incapable of countering him, then he has every right to drop kick your nexus.
Ultimately, TT games seem to come down to whichever team can get their first 2 legendary tier items first. Shut down a trynd/leesin/jax early and even if they try to turtle, you can still win.