The wrap on Quinn was inconsistent conditioning, and relatively subpar lower body. He sometimes had a reverse Platz thing happening - great, great upper, small lower. Also bad timing, mid 80's - 90's just had so much talent.
He placed top 10 at the Olympia multiple times, back when doing so (automatic qualification for the next year's show) was more prestigious than winning lower-tier contests. Quinn, like many others, competed only at the O.
The fact that Quinn did so well, against competition like that, shows he was one of the best in the world. No wonder the WBF made him one of its early signees.