I'm for an early suspect. People keep comparing mence to lucario/aegi, and both of those got suspects. Lets face it, it's not the strongest thing in OU. M-Pinsir outdamages it from the start, and with swords dance it gets stronger faster. Admittedly it's typing and movepool are both better than pinsirs, and it has more speed (+DD), and decent SpAtk (for a mega) allowing it to play a bigger variety of roles than most birdspammers.
It also has few checks/counters, though they are there. It forces a lot of switches and can gain quick momentum from these, often deciding the game if it's allowed to this enough, especially since it's decent bulk allows it to switch in and out without getting crippled.
Most of these qualities can be found on other birspammers/megas, but mence just pushes it a little bit too far.
On the other hand, I honestly I feel as though the ORAS ladder doesn't reflect how the meta will shape out. It's full over people being over prepared for mence, without even trying to play around it with a proper team. I often see people with an ice shard user and a gimmicky scarfer, or another ice sharder on the same team, just to "counter" mence. Just like any other mon, mence can be played around, and isn't as immediately over powering or broken as lucario/gengar. It sorely misses SD and priority (yes it's a big deal, just imagine what this thing would be like with quick attack, or god forbid, ESpeed), and just isn't quite a nuke.
Ultimately, though I don't think mence quite as broken as mons like skymin/gar/khan have been in the past, I think that mence is overall going to be over-centralizing, especially with it's brothers in birdspam to back it up. But I feel we need time to make sure, time well spent without gimmicky checks on every team. Definitely unhealthy for the meta, but it doesn't deserve the bandwagon bitching that's all over this thread.
Early Suspect
EDIT: Also, can we stop comparing this to Base-Rayquaza? Ray can hold an item, has better offenses on both ends, and has a way better movepool. That's almost like saying Phione is the equal to Manaphy.