I feel your pain. If you can, you might try using PimaxXR (which also requires Open Composite for non OpenXR games), it does have an option for forcing only the 1:2 motion smoothing. You do have to click the little picture of the PimaxXR logo as it is entirely an advanced/developer option and can have negative results if not used properly.
Keep in mind that even then it will be dropping frames when the frame rate is less than 1/2 of that of your HMD, but perhaps that’s preferable. You’ll note that it also has sliders to adjust how quickly the rates are triggered as well.
The key advantage of PimaxXR is that is has correct timing of whether to use 1:3 mode at all, as PiTool/SteamVR forces the 1:3 motion smoothing mode FAR too early and stays there for far to long. It is a known bug, and one that the devs are looking into. As an example with PiTool/SteamVR currently you can have a stable 50 FPS and it will trigger 1:3 motion smoothing mode.
See this post for how it went down: Pitool has Sub-Optimal Timing: Motion Smoothing (Originally Titled: Something changed with Pitool on version .271 and forward)
In either case, I’ve messaged the Pimax’s support team to encourage fixing the timing and/or allowing us to disable 1:3 motion smoothing.