OP,
First, a bit of sympathy. Then, a bit of a challenge.
I totally feel your pain. I have been the higher-rated player at 5.5, 6.5 and now 7.5 ladies combo. I have been smoked by experienced opponents who ganged up on my partner, and you are right that it isn't fun.
Making matters worse for you is that ratings come out soon, and you may have faced two 4.0s in 3.5 clothing. So you have permission to sulk, but only for about twenty minutes.
So much for the sympathy. Now let's talk challenge.
I say you should keep playing 7.5, with this partner and other partners. Playing combo is very good for your game. It will sharpen your ability to diagnose the match, quickly. You will need to figure out your partner's strengths and use them to maximum advantage while also figuring out how to exploit your opponent's weaknesses. You will need to dominate the play, finishing the point at the first conceivable opportunity. If you took a double-bagel beatdown, that suggests you have some real work to do in these areas.
This time, it sounds like you had a 3.5 partner with no groundies/passing shots and minimal volleys. Your opponents targeted and isolated her, and there was little you could do.
When this happens to me, I try to disrupt my opponents. Make them less confident about exactly how they could get the ball to your partner. There is no way your partner will begin producing strokes she doesn't have, so you need to focus more on tactics and strategies you can execute as a team.
There are two easy ways to do this. One is with signaled poaches. Once you two start signaling (with the net player throwing a fake every time she signals stay), a lot of opponents will start to freak out. They will change their return, and that is enough to generate errors.
The other thing you could have tried was Aussie. Aussie (where both of you line up on the same side and the server crosses to cover the DTL) is a blessing when you have a net player who cannot volley. You can put your partner's FH volley in the middle for the entire match. You can challenge your opponents to hit unfamiliar returns, with court geometry working against them.
Another thing you personally can try is starting every point at net from a different position. I have turned around matches by starting in no man's land. Opponents aren't sure what I am going to do, which throws them off. (Sure, they could rip a groundie at my feet, except they aren't capable of ripping anything at anyone's feet.)
Also good is what a friend of mine calls "The Pterodactyl" (sp?). When your partner steps up to serve, you have one foot in the alley. As the serve is on its way, you slowly creep toward the middle, splitting when the opponent hits. Visually, this movement seems to close the return window for the returner more than it actually does -- kind of like a huge bird of prey swooping in for the kill. The returner will suddenly be confused about whether to try to go behind you, squeeze a better angle, or lob.
Also, consider your serve order. Combo teams often have the 4.0 serve first for no other reason than she is the 4.0. This is often a mistake. The 3.5 surely knows how to serve. She may not be quite as good as poaching as you are (or should be). The stronger formation often is the 3.5 serving and the 4.0 being a nuisance at the net.
I guess my point is that when you play combo with a weak partner, you have to rummage through your entire tool kit. If you get to the end of the match and you have used all of your "tricks," then the match just wasn't winnable.
