Numbers wise they are close, but Johnson effectively played two more seasons than Brown--unless you want to count his one game last year. Beyond that, I don't even think it's close between the two receivers.
PFR's Hall of Fame monitor has Brown significantly above Johnson
https://www.pro-football-reference.com/hof/hofm_WR.htm. I agree with this metric. While Johnson was good, he was never recognized as the best in the game as Brown was for several seasons. In fact, Brown was recognized as one of the top-10 players in the entire league during the prime of his career. Some other highlights:
Brown had 6 seasons in the top 10 in receptions to only 3 for Johnson.
Both were in the top 10 for receiving yards five times.
Brown had 5 seasons in the top 10 in receiving touchdowns to only 3 for Johnson.
Brown was first-time All Pro 4 times, twice for Johnson.