First off, to say Dylan or the Beatles are overrated is absurd--unless the idea is someone says they are god and no one is god and so therefore they are overrated. Also, I'd define "overrated" as an artist that is seemingly getting first tier classification among fans, critics while more deserved of third tier.
This is, of course, all opinion. So before I'd throw Dylan, Beatles, Floyd, Stones in the mix I'd start with these candidates:
REM
U2 (in terms of full body of work. Several albums are evidence of tier one status).
Adele.
By the way, I think Adele is first tier worthy but her works are all shouty and overblown. She has the talent but her output and artistry are third tier in my opinion.