Tryndamere needs a rework
Rework his rage bar so that he gains 2 rage from attacking (down from 5), 2 rage from critting (down from 5), 5 range from killing a unit (down from 10) but give him 2 fury for taking damage from a minion and 4 fury for taking damage from a champion (does not count against AoE damage).
This will give him counterplay as the other players can simply ignore him to help keep his bar low.
Spinning slash should not lower its cooldown when getting a crit. A fed trynd is unstoppable outside of champions chain CC'ing him, and that's if they weren't killed by the enemy team and PLEASE THINK OF THE BRONZIES, WE CANNOT COORDINATE OK? All those crit strikes mid+ game and the sticking power from his spinning slash is too hard for normal players to deal with, especially squishies who are skillshot-reliant.
Rework Tryndamere so that his ult decreases to the same duration as a Kayle ult, maybe give him a shorter CD on his ult to compensate. This gives more counterplay other than "find some way to stall him for 5 seconds and be sure he doesn't E out".
EDIT: OK the R rework was a bit harsh, so to be even more interesting give his R the normal 5 second duration - BUT as soon as he would have hit 0 health to reduce the duration to 2 seconds from that point (whichever runs out sooner).

) he is heavily gated due to his lack of mobility and how easy he is to kite.