I can't say I've cared to look too closely at the matchmaking to try to understand it... but I want to assume it's pretty 'first come, first serve' and if you're not seeing people in the 1000+ server range show up very often then it's just because 90% of the servers out there right now are not in that range...

Similar to what Malachorn said, I been running into a lot of S2, S25 or 24, one of the 2. Some in the 100s, and occasionally people from the 700s.

i'm in server 302 and i meet people from any server. it's just full random.

Yeah, maybe it is random. Actually, I wouldn't mind if not for the fact that the event opened for just a few hours. If it is always open like normal arena, then no problem. The event is good, but the matchmaking algorithm seems worse than swb/matsuri. It's like it has no balancing mechanism.

The queue is similar to how normal arena (based on observations on meeting people outside my xserver bracket) and bonds. All of the servers in your region is capable of being queued together. Bonds is different as it will match based on various factors such as rank, power, and who is available which happens for me whales - which is a RIP moment. Seems like 3v3 doesn't have any of these factors as me and several others have pointed out that they meet people from older and newer servers and they happen to be running all type of teams ranging from team 7 to edo hiruzen blitz.

You also have to consider that newer servers have players that are still learning to play the game and may have ignored the 3v3 without understanding what it is while older servers than you already went through that process.