I think it does impact his legacy considerably.
When Kobe won his first titles, he didn't get the respect for it because everybody said Kobe was the Robin to Shaq's Batman. When Shaq left and Kobe came back to win more titles, then I think that shut up all but the most hardcore Kobe haters/critics.
When Lebron joined Wade in Miami, Wade already had a championship ring so he had proven he was a winner. At the time he was, arguably, every bit as good a player as Lebron was. Lebron win two rings there, but he often folded in crunch time while Wade tended to be the guy who would step up and carry the team. I still consider those titles to be just as much credit to Wade (maybe more) as they were to Lebron.
Now Lebron left Miami, has come to a Cleveland team that was arguably just as talented as the Miami team before, and he hasn't been able to get that ring. Wade has three rings, Lebron has two. Until Lebron earns one of his own WITHOUT Wade, I will always maintain that Lebron doesn't have what it takes to truly carry a team to a championship.
Now Lebron is ageing and while he is obviously still a great player, it's clear that he's not able to dominate at will the way he could a year ago. He's on a team that is WAY above the cap with little to no flexibility to add talent.
His window to winning a title is, once again, shrinking down around him. If he stays in Cleveland, there's a good chance he'll never win a title again - hard to say if he'll even make it back to the finals again. If he leaves, he has to risk taking another year or two to establish chemistry AND it'll be further fuel to the fire for all the people out there who hate on Lebron for running with his tail between his legs ever time he sees tough times coming.
Now I don't care about rings the way so many people do. I think players deserve individual credit for their greatness, as well as credit for their team's success. Whether he wins another title or not, I will still label Lebron as one of the greatest players ever to play the game. I don't like or respect him as a person, but I appreciate and respect his talent.