Don't Need Le'Veon To Win Super Bowl

... Says Pittsburgh Mayor

Here's a sign Le'Veon Bell's holdout has probably gone on too long ...

Bill Peduto -- the mayor of Pittsburgh and a longtime Le'Veon supporter -- tells TMZ Sports he's beginning to think the Steelers don't need the RB to make a Super Bowl run.

"James Conner's proving to be a worthy back and it's a team sport," Bill says. "It's beyond one player."

It's a bit of a surprising claim ... considering Bell has nearly 8,000 yards from scrimmage in 62 career games ... but Bill -- like some of Bell's own teammates -- seems to be fed up with the holdout.

"He's I think getting very bad advice from his manager," Peduto tells us.

"It's getting to the point of a certain tipping point…