It was just Blaziken, Scizor, Medicham, and the Latis in XY and Audino in ORAS. And Medicham had to otherwise the Mega would have been weaker than the base form. That's only 6 out of 48.
And then ZA adds Greninja, Chesnaught, and Dragonite so far. It's not the norm, but ZA's done it an unusual amount just with those 3 out of the currently revealed 10 out of 45.
You forgot Abomasnow, so its 7 out of 48. I get your point though. That being said, out of 3 Megas that started with Levitate, 2 ended up retaining it. In SM those became 2 out of 2, since base Gengar lost it. Levitate Mons very rarely get a second ability in first place, Bronzong and Weezing are exceptions, not the norm.





