I had a Waterproof D9X when I got my Seaskin trilam. The D9X is breathable.
To me, the issue is not about how warm the water is. It's how warm the surface air is. But, maybe I have not dived dry in warm enough water.
Anyway, the breathable suit is a little more comfy to be wearing during a surface interval on a hot day. But, it's not enough of a difference to make me want another breathable suit. It works for me to just take the top half of the suit off.
If the water is warm, I won't be wearing hardly anything under the suit, so taking the top half off (or taking the whole suit off) keeps me comfy. If the air is hot, but the water is cold, I would be wearing some kind of warm undergarments. In that case, it's the undies that would make me hot, not the shell.
The downside to a breathable suit is that the laminated layer that makes it waterproof but breathable is somewhat fragile. Eventually, it will get worn just from rubbing against you and your undergarments. Then you'll start to have pinhole leaks. I sold my D9X to a buddy and he has already had to find and fix a few of those in the time he's had it. I bought the suit used, but it only had <10 dives on it. I did 52 dives in it. My buddy has had it for close to 2 years now, so I bet he has 100 dives in it.