The sandbagging is definitely a real thing. I'm in a 500 mil GP guild. If we win a 2 or 3 in a row, we'll often get paired with a bigger guild that limits sign-ups. Always with these guys there's a front wall of Tanos, trying to exploit the no buttons bug.
I presume that these guilds have set requisites before you're allowed to sign up, or do it on a rota. I definitely wouldn't want to play like this.
If you're being outmatched, you're unlikely to go against a sandbagging guild. It's when you've won 3 in a row, that you're likely to get one.
I kind of agree that I'm not sure the rewards are worth all that specialisation. The droid brains are good though.