As the owner of a 550EX which doesn't match up to a number of other guitars I own, I'd say yes, they are overrated.
On top of that, honestly, I don't find guitars designed like 550's to appeal anymore. I want a 12" radius. I prefer wilkinson vibratos to Floyds. I don't want or need a super thin neck to shred, I've put the time in and can play faster and cleaner on a thicker neck, with all the extra comfort that provides.
These days, I'm somewhat of the opinion that 550's and suchlike are guitars for people who never outgrew their overriding love of one style of music, and don't play much else. I can't think of any session musicians who use 550s, for one thing. Or if I can, they're players like Rob Marcello, who are very much 80's metal guys. On the other hand, monster players like Guthrie Govan and such, are leaning towards a wiser blend of old and new in their instruments.
With all due respect this is a bit of a "high brow" opinion.
Most session guys will play whatever fits a given scenario. Sure, most lean towards LP's and Strats, but I'd imagine tuning instability would get any Floyd-equipped guitar kicked out of the studio. Even guys like Vai will track with an LP or an SG here and there.
And speaking of Vai last time I checked he was a Zappa level player. Can most session guys claim that? No. Also notable session guy Mike Keneally (also a Zappa guy) played Jems live for a while because it FIT with what he was doing with Vai. If Mike is going to play on, say, Taylor Swift's next record would he bring his Mesa rig and Deathlok-style EMG equipped guitars? I think not.
Yeah, there are a lot of guys who play RG's who remain fond of 80's shred. Nothing wrong with that if it makes them happy. This doesn't make the RG more or less versatile. In fact, you could say the general looking down of noses at guys who play RG's is a bit of gear snobbery. I've had this happen to me and the snobbery gets kicked to the backseat when I switch to position 2 or 4 on the 5 way and kick out a country or reggae lick. Is my RG generally suited to this? Not really as I have high gain pickups on the guitar and my rig is geared more towards rock. It can come somewhat close though.
Sure, I might be biased towards the RG550 as I've been playing RG's for 21 years and I'm posting on a board called Jemsite.
In terms of the original question I do believe the RG is very underrated.