I get it. My experience is strictly valid when motion reprojection is disabled. When you turn it on then the framerates get locked to only those preset rates as you’re explaining. So I can see where even a minor improvement might make the framerate with motion reprojection on jump to the next higher value and thus you experience much improved performance.
I leave MR off in both games because I’ve been able to find smooth game-play as I described but I understand that 30 fps might not be good for some people. That value is for me and you need to find what’s best for you. The major point is the framerate consistency. That’s what motion reprojection does. It fills in frames so you get better consistency.
Unfortunately for me I get bad artifacting with it on, moreso in MSFS than DCS, but if I can get satisfactory performace with it off then I do that. And luckily I’ve been able to get great performance with it off. In MSFS I’m running with 85% resolution in OpenXR and 100% in-game. So I’m getting a great picture on top of the great performance.