Have the same problem, and it is after the "BIG" update, im currently running at 2 Fps with frame latency of 850 ms. I'm using oficial optical Oculus 2 cable.
I'm lost at the moment specially that I've noticed that it makes almost no difference what settings I'm running in DCS, also when I check my CPu and GPU load it hovers around 35% on both.
I'm starting to think that it is on Dcs side, Il-2 Sturmovik i have cranked up to max (ultra settings) and it is not dipping below 45fps, same thing with Project Cars 2.
Pc Ryzen 3600, 32Gb ram, 2080 8Gb, on M.2 Nvme.