GSP is the greatest welterweight of all-time for sure, but the greatest fighter of all time seems kind of iffy and beating Michael Bisping isn't something that should cement that legacy, Bisping isn't very good he beat basically one top 5 guy in his division once in his entire career, got the belt off that single win and ran and hid from every credible challenger. I'll give George a lot more props if he can beat Woodley or Whitaker who are guys I think are actually worthy of holding a belt.
It was nice seeing GSP again and see how he added some wrinkles to his game (like a strong left hook), he's got a few more things to look out for now, but he did seem to gas when it was never an issue for him in the past and he was slow on his exits from exchanges, against better competition that will be an issue.