I love Dez, but at the time there was no WR I'd have taken over Michael Irvin, and that includes Rice. Jerry Rice was a better receiver, but Irvin was the heart of the team IMO. Dez is vastly more gifted physically - but while Irvin was almost never the best athlete on the field, he was almost always the best WR.
Irvin couldn't sky and fight for the ball the way Dez can and while strong he wasn't as hard to tackle as Dez, but he was a great route runner and he was as tough as they came.
So no, to this point Dez hasn't quite lived up to the Irvin standard - but there is no shame in that, very few guys ever have IMO.
I was too young to have really seen Pearson, I was only a kid when he played, so I can't compare them directly.