Montana played longer, but was also injured more often, statistically speaking. Young had a better career according to QB metrics by a meaningful amount and ran much better.
https://bleacherreport.com/articles/...an-joe-montana
From 1991 to 1998, Young's average passer rating was 100.9. In fact, from 1991 to 1998, every other quarterback in the NFL combined to top a 100 passer rating just four times—three of them were in 1998.