in 15 months, there would have been 5 4* characters (1 every quarter),
a new 3* every second week,
a new 2* every now and then (so far, 3 months)
This pace will be the same for awhile I think.
Most of the 3* characters will never enter the metagame for a reason I can’t explain. Looks like they are popular/fun characters and are used for that matter. To attract new players (since they are advertised on marvel.com).
We may have Ultron when the movie is released. It looks like D3 are closer to marvel.com now, and they’ve had a news article every second week (more or less), so MPQ should be closer to the Marvel “daily life”.