Yes the arena team doesn't automatically disband, but no one wants to leave his personal team rating at lets say 2k, to join a random one at 800rating and then get kicked after some arenas, viceversa no one wants to join a high team rating and have a gap between the personal and the team rating that probably will never catch up. "Oh we did 2050 I can buy shoulders, JK i have personal at 1400 we need to do 2300 rating".
About SQ, yes the intention was "supplement" a dieing bracket, but it ended up replacing it. Every player I inspect has highest rating in SQ, maybe some 2s, but 3s is for sure the lowest one.
Again, I have no data to "prove" you that the majority or people play Blackrock just for SQ, but just look at the ladder, 3v3 top team is 2500 and lowest is 1800, SQ is 3000 and lowest is 2600...
Its not about RNG you keep missing the point, its about balancing the things, since SQ is, at all effects, a competitive bracket, players that come from Icecrown, or Lordaeron, or whatever server, and click "Template NPC", and go 3x Battlegrounds, shouldnt NOT be allowed in SQ until certain arena experience. This is the main point.