Since when has there been no cap for Superstar potential?
Well there is, but it's around 130k - 190k. Since this fella is in his late 20s, he would probably train like a turtle before reaching his cap. Also, the guy training him is in 4th league and even if in 4-5 seasons reaches 2nd league, for instance, I doubt he will be needing a 200k monster.
Speaking of 200k salary monsters, I prefer a 120k - 150k one with good secondaries if I have to choose.