I guess it depends on your definition of small, because Bret and HBK were considered small at the time they were champions, as was Macho in the 80s. It's probably true that Bryan only got his WM main event due to Punk leaving, but it's not like Bryan wasn't a featured guy that had already headlined PPVs as champion before.
Even if Bryan never had his WM moment, it would be silly to say he didn't have a successful career in WWE, and he's pretty small. The exceptional talents always rise, in any era. And the size of wrestlers has dwindled for years. This is an era where Roman Reigns is considered a big man, despite being smaller than Billy Gunn, who would have been laughed at in the 80s.