as to the number of pass plays called, on a league-wide basis, from the relevant eras?
I could be completely wrong, but my guess is that a lot fewer passes were thrown throughout the league when Brown played than when Marvin Harrison played.
That's not to say, of course, that Harrison isn't Hall-worthy, or that Brown is more worthy than Harrison. I also realize that the careers of Brown and Harrison overlapped to a degree. But we're seemingly still in the midst of a remarkable transformation of offensive football in the NFL, at least in terms of the percentage breakdown between runs and passes, not to mention the number of plays in a game, due to no-huddle and hurry-up offenses.
If people are going throw out raw numbers like number of passes caught as if that's an apples-to-apples comparison between players of different eras, then we may as well not have the conversation.
For better or worse, catching 100 passes in a season or 1,000 passes in a career -- while both outstanding accomplishes -- aren't nearly as rare as they used to be.