Biggest problem for Barrasso is what a yo-yo his career was. One of the most inconsistent goalies ever. When he was healthy and his head was in the right place, he was one of the best in the game. But he was injury-prone and his career ended being all over the place.
His first 2 seasons (83-85), he was brilliant - best performance by a teenaged goalie in NHL history.
The next 5 years after that (1985-1990), he had one excellent year in 1987-88. The other 4 years he was injured, or performed poorly, or both. Went from hero to zero in Buffalo and punched his ticket out of town with iffy play and grating personality. Take out 87-88, and his GAA over that stretch is around 4.00.
Then, from 1990-1993, he re-establishes himself. Behind a high-scoring Penguin team, he plays terrific goal, and makes a reputation for himself with his great clutch play in the playoffs in Pittsburgh's Cup wins in 1991 and 1992.
After 1993 (Volek!), his career pretty much goes off the rails. Turns in one brilliant season in 1997-98, but other than that, he was awful. Injured all the time and didn't play more that 50 games again. Essentially missed 3 entire seasons through injury. Struggled when he played, and had a couple awful playoffs (1996 vs. Florida stands out) as well.
So what you're left with is a guy who had 5 or 6 really good seasons (1983-85, 1987-88, 1990-93, 1997-98) and about 15 years where he was injured or crap.
A guy like Joseph (who I don't think belongs in the HHOF, for the record), might not have been as good as Barrasso at his best, but you could *always* rely on him to deliver 60 games of quality goaltending for your team, year-in, year-out. You simply can't say the same for Barrasso. The fact that he was average or worse (due to either injuries or poor play) for 3/4 of the seasons in his career really, really hurts.