Presence in pro play indicates viability in meta and Trynd quite frankly is viable in solo q and is not over powered by any standard.
Critical chance as a whole is a rng mechanic, whining about the "rng" crit passive when nearly every adc builds IE and crit items, drakes are rng (inferno, ocean, mountain, cloud) is illogical.
Should we remove crit as a whole because a a Tristana with 25% crit chance may 4 tap a vayne with crits in laning phase?
Trynds ultimate mechanic is still being over simplified by you. When you pop ultimate as Tryndamere you have to decide who you go in on, which abilities are up, sums, cc, account for incoming skill shots. Then its all about dancing around as you jump your target, after you have to decide whether you attempt to go for multiple kills, die because of a misplay, or attempt to stay alive.
"lane completely determined by RNG" - absolutely garbage and untrue, and if such is true than same can be said to all adc's after they build one crit item, Trynd has abilities and apparently you are not aware of them and how they work
"Ultimate ability that removes the vast majority of decision making from the champion" - This is perhaps the most ignorant statement as the ultimate is a complex, unique, one a kind and best feature of the champion
"Trynd's kit removes agency from both players." - Literally how? You are making a random claim with no example or evidence, big words no facts
Claiming that a champion is brainless and is all RNG was your first mistake and unfortunately you have a incredible superiority complex that leads you to believe you think in a higher realm than me and are so much wiser. You were blatantly wrong and exaggerating and instead of sucking up to it you instead try to deflect it.