Crosby had a very bad series, but he is already one of the greatest playoff performers of all time. Nothing he does or doesn't do in the playoffs for the rest of his career will diminish his legacy. Kucherov is a great player - likely a bit better now than Sid is considering their relative ages - but he hasn't proven what Sid has. In that sense, his performance is more damaging to his legacy than Sid's is.
Either way, Kucherov has a long career ahead of him and will have plenty of chances to make up for one lousy series, even if this one was a historic choke by Tampa.