I'll be honest, I don't like tryndamere. His kit has so much power in it, as to the point where it's nearly impossible definitively win lane.
His passive: 35% free crit chance. It's incredibly hard to trade early on, when I know that I die to tryndamere hitting double crits with ignite. Yes, I understand that the counterplay is "Just keep him off minions". That's not always easy, especially if tryndamere counterpicks.
His W: Max rank, 80ad reduction in an AOE around him. I'll admit, I'm surprised that tryndamere doesn't max this first. Excluding the slow, this ability removes roughly 2500g - 3000g worth of stats from everyone around him. It's also a nice slow.
His ult: Just doesn't die. You can't outplay the ult, you can't stun him and burst before he ults like Ekko. You have to hope the tryndamere doesn't ult in time, or doesn't know cast animation like Cho's feast, or Vlad's Hemoplauge. You have to either be able to kite him for the duration, or cc him.
The main thing with tryndamere, he can go 0-10 in lane, and still be incredibly viable in duels and splitpushing. The stats he gets, combined with a period of invulnerability makes him a pain to deal with overall. You can send one person to stall his splitpush, but typically, tryndamere can outrun 1 person.