I definitely witnessed this when I was in year 13 - quite a few people I knew ended up being over-predicted, often in a way that was fairly obvious; at least one person persuaded their teacher to predict them As and Bs (after getting Cs and Ds) at AS... and they ultimately got Cs and Ds at A2. And it does work both ways; I was predicted A*AA and got A*A*A.
With that in mind, I'd really prefer a system where students apply after receiving their final results. I would've benefited from that massively; there weren't any spaces at better universities for my course (Law) on results day. I really like the university that I'm at, and it wasn't worth taking a gap year and re-applying, but I exceed the required grades for my current course (AAB) three times, which is a little frustrating.
The people that were over predicted also would arguably benefit, rather than being given generous predicted grades, leading to offers they can't meet, leading to them battling with clearing on results day. And at the very least, changing to a post-results application system would solve the current issue of admissions tutors not necessarily believing predicted grades (even when ultimately realistic) because so many prove to be wrong.