I think you are mixing two things here : the HOF and the jersey retirements. A jersey retirement is based on the greatness of a player relative to their franchise only. The Hall is for the players that had a significant impact on the game itself for the duration of their career. Those can be coincident, but aren't the same. Pietrangelo is a top-3 defenseman in Blues history and captained their way to their first cup ever, after a 51 years-long wait. From the Blues perspective, he is an all-time great. Letang was the anchor on D for 3 cups, all won by the same core, which was by definition more successful than the Lemieux core (2 cups). From the Pens point of view, he is also an all-time great. Maybe neither will be in the Hall, but their names will be in the rafters.
Btw, the entry to the Hall nor the jersey retirement exclusively depend on individual achievements. Being great, or deserving of fame, doesn't strictly mean being performant. It's more complex, it includes leadership, opportunity, demeanor.
I'll give an example. Richard never won an Art Ross, and I think got the most goals twice. He's got legit HOF stats, don't get me wrong, but why is he the absolute legend people praise? The fire in his eyes, the determination in his steps, the power of his shot, and the passion to win contributed to the creation of a larger-than-life idol. It did translate to actual production on the ice, of course, which will be taken into account for an admission to the Hall and a jersey retirement. But nobody gets to be legendary on account of what's on a score sheet. It's what the player meant to the franchise, to the fans, that makes him unforgettable.
