Everyone parrots the "he was used wrong" thing, but he was pushed pretty strong in 98. Any stronger and he'd be pushed above Nash/Goldberg/Hogan/Sting, which wouldn't make sense because he wasn't as over.
They gave him programs with familiar, over guys like Flair, Perfect, and Macho for his first few months, then turned him heel and gave him maybe the biggest heel spot besides Hogan for the next 6 months. He feuded with Booker, Sting, and DDP for the 2nd half of 98 and got to put a bunch of guys on the shelf storyline wise, including Sting.
His 98 run wasn't bad TV-wise, and he was pretty over when he turned heel, but he wasn't putting on the quality of matches he did in WWF. And looking at the guys he was working with, it's hard to say it was them. DDP and Booker were having great matches with everybody but Bret in 98.