The future is now old man

He beat Kefla though. And its not nearly perfected yet. Whis even said that he's merely dodging with Ultra Instinct, he hasn't taken attack form yet.

Not to mention that he has only had the form for minutes. You can't expect him to beat Jiren, someone who's seemingly already a master of that kind of power. Besides, how cliche would that have been?

They've been using the deus ex machina cliche the entire series though