There isn't a ball that is going to do much for a steep downswing. That's just something you need to correct. Though something that compresses more is going to be marginally better than something you are not compressing. You are most likely barely putting a dent in the ProV, which means it is rolling up the face, drastically increasing backspin and costing you a lot of distance. Steep results in an inefficient energy transfer. You want that energy going down range, not up the face. The cleanest energy transfer with driver happens with impact occurring on the upswing. You are doing the opposite of that.
The answer to your question is the 330RX. For starters, a urethane cover combined with a soft core makes it feel very soft putting; the softest you will find. I find it spins well on full swing shots but I like even more that it doesn't over spin, specifically around the green. If you like something that really grabs on the second and third hops when chipping, then you would want the RXS. Personally, I like the ball to release a bit more. But the thing that sets the RX apart from other urethane cover balls is how many more fairways you will hit. If you swing hard, you'll likely give up a few yards on best swing to best swing comparison with Prov1 (maybe 3-6 yards, not much), but you will absolutely without question average longer and hit a lot more fairways. Track it. I guarantee it. The feel takes a little getting used to as you are used to playing a hard ball that you are not fully compressing. The RX core is softer, so you will compress it more fully, more frequently, which is only going to be a good thing. The bottom line is that the RX protects you from your misses better than any other urethane covered ball made. A lot more. Bridgestone's "best ball ever" campaign came about because R&D met with marketing and said to them, "this is the best golf ball ever made." The campaign is for all four 330 balls, all of which test well, but the RX is the one that really separates itself from the competition for most players. Truly a game-changing ball.
I would discourage anybody from playing the e7. It's a rock and doesn't do anybody any favors. It's good for long-drive competitions and that's about it. They also stopped making it, which is probably why you can't find it.