I don't think it hurts it that much. Fact is, they were far overmatched by a superior team. That's not his fault, and at the very least, he played a good series and did what he could. The only one that really hurts his legacy was the loss to Dallas, because he didn't exactly have a stellar series, regardless of the fact that Dallas was a better team. At least in this series, he did what he could.
Being very overlooked, is how awful of a coach Spoelstra is, and the effect it had on this series. Especially when it comes to defensive adjustments, and his poor management of Wade.