I'm in a 700M gp guild.
I don't mind people wanting different/better matchmaking, but I feel compelled to say that in our guild -- and I imagine in many guilds accused of sandbagging -- the number of players joined has nothing to do with wanting to get favourable matchups and everything to do with the fact that there's a lot to do in the game, there aren't many players with 14Mgp to match our average, and not everyone you want to recruit is interested in all phases of the game.
On top of that, we have some players that have been in our guild for a long time that have stopped signing up for TW. Many older players still like aspects of the game, but as they lose patience with CG's changes, they are less and less willing to play the parts of the game they don't like as much. They're seeking an experience closer to what they enjoyed years ago, and for whatever reason (often but not always datacron chasing and/or having to place guild-priority Omicrons when they'd rather save those for GAC or whatever) TW isn't it.
I keep reading posts on the forum that tiptoe up to the line of accusing guilds of cheating. In my experience that's not it at all. Some people just don't like TW and there aren't enough that take it seriously to fill all the roster slots in high-end guilds.
Whatever is going on with matchmaking and however much you like/ tolerate/ hate it, it's not the fault of the guilds.