You are describing a catch-up mechanic.
What you don't realize is that mobileshits have a monetary reason to not introduce that sort of thing.
They make money when you buy crystals and rolls, why would they give you multiple SRs, particularly 5* SRs, when a lot of people would wear down and just spend money or leave?
The only welfare SR characters they're going to give are from events and most of the time are just useful as warm bodies or alt skins for the SSR versions.