When I talk about the SF "problem" (they get capped with minor salaries than the rest of positions is a simple observation, I dont know why it happens, simply.. it happens). I suggest everybody here to search some info about SF and compare their limits with the PGs.
Observationally, you identify "capped" as a "slowdown in training speeds". There are various reasons why training may slow down. I have no evidence that SFs cap any differently from other positions -- using your logic, my star SF should have capped "way below" the normal 35k cap for stars, He has an actual salary of above 20k and is definitely not capped.
"I don't know half of you half as well as I should like; and I like less than half of you half as well as you deserve."