Well, in the manga, Yuji has a lot of growth and potential. However, Mahito is no pushover. His cursed spirit nature and devious tactics make him a force to be reckoned with. So, it's hard to say for sure who's stronger.
Itadori did indeed die in the manga. His death had a significant impact on the story and the other characters. It was a turning point that led to many new developments in the plot.