Why yujo was extremely important.

If it wasnt for yujo the series would've been over by now.

There is 2 narrative reasons for yujo to exist and 2 in story reasons

The 2 narrative ones being 1. To complete yuta's character arc 2. To show the extent by which gojo's "friend" treated him as just another person

The 2 instory reasons are 1. To protect yuji and todo from sukuna's domain. 2. It helped yuji realise the error in his cog mentality and allowed him to move on.

Yuji only gave up his cog mentality AFTER choso's death meaning the only time he had to ponder over this was during yujo vs sukuna. If it wasnt for those 3 or so minutes i doubt yuji wouldve been able to realise his true self and in so achieve domain expansion

Maybe i'm wrong but i think this makes sense

TLDR: yujo gave yuji time to come up with his new philosophy and achieve DE