@walmis I may add a data point here. I always use (and recommend) external fps limiter (Afterburner/Rive in my case). My ingame is also set to 180 fps (default), but I'm factual limited to 120 fps by Aftrerburner.
i set back to 180 FPS and it works now if you see i get around 140FPS and when i switch back to telemFFB windowd DCS is at 60FPS. i am not sure if this help you
Part of the reasoning is, that the ingame fps limit is governed by the main render thread on the CPU. I found it should have better things to do than limit the fps. Better leave that to the GPU driver or similar.