Lebron has never lost in the 1st round of the playoffs and he has only missed the playoffs his first 2 seasons.
So with that in mind, what is better for Lebron's legacy, to miss the playoffs or to make the playoffs but get hammered by the Warriors in the 1st round? In other words, is Lebron better off keeping his playoff streak alive or his 2nd round streak alive where his legacy is concerned?
I think in the grand scheme of things in judging his legacy, neither is going to move the needle.
Personally, I only think extreme winning/playoff success moves the needle, something LeBron isn't anywhere near. We're talking Bill Russell 11 NBA championships in 13 years, 2 NCAA championships in 3 years, levels of success. Obviously this has helped Russell's legacy.
But for everybody else, as long as you have some championship pedigree, it doesn't really matter.
Does anybody think less of Kobe because he missed the playoffs in '05 and got eliminated in the first round in '06 and '07? Or Duncan who got eliminated in the first round in '09, '11, '15. Magic and Kareem both lost in the first round in '81. Kareem didn't make the playoffs in '75 (missed a few games and team was 3-14 without him, 35-30 with him) or '76 (healthy), and had a first round knockout in '78. Bird, still All-NBA 2nd team level, got knocked out in the first round in '90. Hakeem missed the playoffs in '91, and had many first round knockouts ('85, '88, '89, '90, '91, '98, '99, '02). And some of these are guys who get some argument for greatest all time, but all are at least universally considered top-3, top-5, top-10, top-15 all time.
Either way, sure the talking heads might bring it up the next day after it happens, but afterwards it won't really be considered when it comes to legacy.