Sure you can compare them - that being, them at this stage in their careers. Again, it seems people default to this logic that Vince is a 10 year pro or something. Why can't he develop further too? If you don't think he will, fine, but that doesn't mean he can't or won't in reality.
Steve was a great passer....in 1AA. When he came to the NFL, he took a while before he was able to make the more complex reads and rely on his arm more than his leg. Vince was run-before-pass for a lot of his college career, but he was also playing tougher competition. Who knows what type of college QB Steve would have been at Texas.
Of course VY has a lot of work to do, but Steve had a lot of work to do too. He took years and years to reach a point where the Titans offense wasn't 50% handing off to Eddie George, 50% checking down to Frank Wychek. Years. And he too was quickly labelled a guy who couldn't and wouldn't. Maybe not to the degree VY has, but then the media and fan discussion mediums have developed a lot since the mid to late 90's.
Steve had about 100x the mental and physical toughness than VY has shown so far, but that doesn't mean Vince can't become a better passer.