I had a chance to take the 1911 back to the range and tried shooting it with my thumb up on the safety rather than below. Not much else to say besides "thumbs up." It was great, and I shot well, I'm very happy. I'll probably change the grips eventually but I haven't done it yet.
I gave it a try
The CZ is just very different from the 1911 and there's literally physically no way that I can get a two-handed grip on the gun if my thumb is higher than that "thumb rest." I'm not going to complain about it even if it looks wrong, because on a good day I can shoot a 3-inch group with the CZ.
And this is unfortunately what happens if I move my thumb above the thumb rest, a big gap in between my hands, which does not work at all. This is the RH shot but it looks the same LH if I move my thumb that high: