Hello Riot, Since you are busy with a ton of stuff I shall make this short. Tryndamere is a perfectly balanced champ except for his ultimate, 'Undying Rage'. To make it balanced all I suggest is while he is ulting he should not be able to crit. That will, in my opinion, make it balanced.
Cheers!
How to counter post-6 Tryndamere:
Then you have just gutted him that way, simply reduce the duration of Undying Rage by like a sec or so, or make it like 3/4/5 second duration with lvl 6/11/18 would be cool imo.
He just needs to be redesigned in my honest opinion. His ult and his overall kit are really poorly designed.
He has to auto you to death. Sure he can crit a lot and has some decent sustain, but if he isn't fed he is just a ly that you can swat.
Rock solid counter 
I think he's unbalanced in the sense that he can cast his ultimate WHILE stunned. The concept of chain stunning him so that he can't use his ult, is negated because he can use his ult while stunned.
