Now he's easier to peel in a team fight because he can't spin or shout while ulting, however the ult lasts long enough so that chain cc is far less effective at denying Tryndamere auto attacks than simply disengaging hard.
He may not have any slows or dashes of his own but his team might, which makes using your ultimate more rewarding if you have a team that can support you with vital crowd control. The point is he is a better team fighter, but he isn't nearly as overbearing as a duelist anymore because he can't stick to targets while ulting without allied help.
He isn't as overbearing in a split push anymore because a Tryndamere that can't use abilities is one that isn't that hard to run from-- just make some distance and he has no real way to close it.
It tones down his split push and moves power into his ability to team fight. I'm a die hard Tryndamere player, with about four thousand Tryndamere games and I'd gladly give up split pushing power in order to have the option to team fight.
Besides, currently Tryndamere played optimally tries his best to not interact with the enemy team at all-- he just split pushes and runs when trouble stirs or uses undying rage + massive sticking power to kill the person trying to stop him. That is really boring to play as and play against.
With this change he would rely on his team and would be required to interact with the enemy team in a team fight in order to access his power. Would you rather end up losing to a Tryndamere who you never even had the chance to fight, or lose to one who you actually were able to deny multiple times in a team fight? The point is this change would make Tryndamere less unfun to fight against / more interesting to play.