Tryndamere is actually a playable siege minion from the Baron-Banner days.
Seriously though, he brings very little to the table that Master Yi doesn't already.
Tryn's Passive and Q grant him critical strike chance and attack damage while attacking? Yi's passive gives him an extra auto-attack which helps with critting more often with the sheer density of autos he makes, E grants bonus AD, and R provides attack speed.
Tryn's Q heals him? So does Yi's W, and it even grants him damage mitigation while healing more health.
Tryn's W slows OR negates resistances? Yi can catch people with Q and R, while negating resistances with E.
Tryn's E can help him go through walls? Ok, he has that, though Yi's Q bypassing skillshots and popping projectiles like old school Flash gives that a run for its money.
Tryn's R--the most iconic thing about his entire kit--is even outclassed through the use of two of Yi's skills. In almost every instance where a Tryn R is viable, smart use of Yi's Q, W, and R do the same and with more manageable cooldowns.
At this point, they may as well rework him again.