A lot of things have changed in the NFL since then.
This topic is fascinating to me and I wish an in depth podcast was done on the subject.
In the off-season, Brady said that he thought NFL coordinators were dumbing NFL offenses down to allow college QBs to come in and contribute faster. I agree with him. Take a look back at how long it took for past QBs to contribute and become elite. Look up Dan Fouts, Warren Moon, Steve Young, etc. None of them were good right away. A case could be made that the Steelers won their first Super Bowl in spite of Terry Bradshaw.
While defenses are more complex now (mixing of systems), all 4 offensive systems were fully developed by the time Jim Kelly was calling his own plays. The development after Kelly was the mixing of systems.
A strong case could be made that Kelly was among the fastest accurate decision makers of all time. He ran a run'and'shoot offense, which is just a sight adjustment offense. He made some of the quickest pre- and post-snap reads I've ever witnessed.
I think QBs like Kelly, Aikman, Elway, Marino, Montana, Young, Favre, etc. could come into today's NFL and be elite right away with how the reads have been simplified and modified to look like the college game. Of course, aside from Elway and Young, none of those guys could move like today's QBs. But I think the play calling may have been more advanced and the reads more difficult in past versions of the NFL.
It's worth a really good podcast with maybe Belichick (to talk defenses), Brady, Elway, Marino, and some offensive play callers from the time like Holmgren and Gruden.