Borderline all stars don't win championships.
We pick the winners to be allstars and dub them "stars." Players with similar stats, capabilities, etc, on lesser teams are foregone. So you could argue that championships leads allstars as much as allstars leading to championships.
The Pistons had one allstar before their championship (B. Wallace), four after (Billips, Hamilton, B. Wallace, R. Wallace). Were these three guys that much better individually during their championship year, or were they rewarded for being major contributors to a championship team? You know the answer to the question: how many allstar games would Hamilton have made if had a career with the Timberwolves or Kings?
Imagine Duncan drafted by the Clippers who make the playoffs a few times but never get past the second round. Would he be in the "all-time great" category? Or would we be saying "well, he has really great talent but could not translate that into championships because he could not take over a game like MJ or Kobe?"
Or imagine Dominique Wilkins drafted by the Celtics. Not hard to imagine him being in the "all-time top 10" players list and citing him as the reason for their titles.
So it is easy to say "you must have a superstar to win a title" because we dub our champions as superstars. It becomes a tautology.