I think I figured this out. Looks like DCS is only able to run VR at 45 or 90 fps (I don't think it can even tell it's a Quest 2 headset, it just assumes it's Rift S). Quest 2 default for Air link is 72 Hz and that doesn't mix well with 45/90. After I switched to 90 Hz in Oculus settings the stuttering went away. Still I have no idea how this didn't affect F18 or any of the FC3 planes, just the A10C2.
PS
One explanation could be that this resynchronization from 45/90 to 72 takes an extra toll on the GPU. With simpler planes I was at the point where my GPU could still handle this, but with A10C2 it was just the last drop that pushed the GPU over the edge.
PPS
In the end it looks like it's simply a Quest 2 tracking issue, which occurs under high load of all components involved when using Air Link. If this stuttering starts to happen, the simplest way to resolve it is by just pausing the game and taking the headset off for a second to reset room-scale tracking on Quest level. With lower bit rates, simpler missions and planes, lower rendering resolution this is a non-issue, doesn't happen. With everything cranked up and when the mission starts in some cluttered environment in a more complex plane like A10C2...
