It would be interesting to compare the dropped passes and fumbles at the same point in their careers. I don't know how to look that up but I bet Irvin has less in both.
Also, Michael had Emmitt to carry the load during games, so he saw less opportunities. It isn't fair to compare the two different eras, totally different offenses(minus this season).
Irvin knew how to use his body and hands very well to get position for a catch, Dez uses his elite athletic ability to go get it. Irvin also ran precise routes, clean and crisp. Not saying Dez doesn't now, he is getting better.
Irvin was a better technical receiver and Dez may very well develop those same skills.
I would love to have seen Michael play with Romo and this offense(again, minus this season)........his numbers would dwarf Bryant's IMO.