Tom Brady has been in the league for 20 yrs and quarterbacks in general have incredibly long careers compared to CBs so that's not a great comparison. (I'd Also take Mahomes over Brady next year but that's a different discussion).Best performance from a corner for a single year is not the same as being the best corner in the league. In terms you'd agree with: There have been NFL MVP QBs who had better years than Tom Brady. Does that mean they're the best QB in the league?
Corners don't sustain dominant levels of play for years at a time, Revis was arguably the best corner in the league as late as 2014 and he was out of the league after 2016/2017.