Wow, I'd highly recommend you speak to a coach about this shot. I won't even try to give you advice on the technique as it's so tough!
I would say this though, don't be so quick to dis-count the slice. A bit of creative slicing can go a long way, especially if you're a one-hander and they're hitting to your backhand with heavy top-spin...it kicks up awkwardly for a backhand drive but nicely for an attacking slice high to low.
Just hit the shot you feel most comfortable with I'd say. If it feels awkward to hit a drive, then be creative (easier said than done, I know!).
I would just stop complaining and use the slice but I'm not getting anywhere with a regular deep slice. Of course in the past when I played against weaker opponents, the slice would be useful since they wouldn't be able to handle a low skidding ball, but the slice against the top players doesn't do much unless I angle it pretty nicely, but that is quite difficult to pull off unless I'm in a good position off the court to do so.
Don't try to hit flat. Loop it back with a lot of spin.
That isn't the problem. The problem is to hit the ball cleanly when it is high in the first place. I'm not asking whether I should hit the ball flatter or with topspin, I know that. The problem I find with the one-hander compared to the two-hander is the backswing. With the two-hander, you can have a short backswing and muscle through most shots that you need two, but with the one-hander it is tough to hit the ball firmly without a good, full backswing. So when I play somebody who uses a lot of topspin, they'll first hit the ball flat to my backhand which is fine, and then they'll throw in a heavily topspin shot which then sometimes make the ball just sit there on the bounce taking like what seems like an eternity to kick up causing me mistime the backswing.
My backhand plays extremely well against people who play pretty flat through most of their game since the ball stays low enough to always be at my hitting zone. But the other day, I played against the number 3 in our US region-division who uses quite a lot of topspin especially off the forehand side and my regular flat/topspin backhand was horrible in that match and was probably the only thing that cost me which got me thinking on what I could do.