No worries at all I hope it helps! I'm still learning a lot myself from people who know way more about this than I do.
One of the things with better PiTool / SVR balance is that it now gives me enough GPU / CPU headroom, which I didn't really have before, to allow for in-game HMD 1.25 - this in turn sharpens things but also improves on techniques like Fixed Forward Rendering (PiTool + RTX card can enable and reduce quality outside of your vision, reducing overhead further).
GPU is number one naturally, but both can have an impact esp on primarily single core apps like DCSW. Steam can give you additional granularity yes, and more so via the config instead of the UI. Hence me fixing the SS value at 0.25. Any other value with PT x2 would lead to less accurate pixel mapping, and therefore more alias / shimmer etc. Relying purely on a high SS value to improve quality is a brute force method that will tax your GPU to the maximum.
Re in-game values, my understanding is that that while you can also use Elite's in-game SS and technically get a benefit, it's less efficient for VR. So personally, I stick to an in-game HMD bump only for VR, and in-game SS for monitors. Via EDProfiler in my case.
I assume there must be some additional overhead to running any 3rd party platform, regardless of efficiency. All pros and cons, it will depend if the Oculus settings alone give enough of a satisfactory boost with pixel-to-pixel mapping while keeping the hit low. Can't comment on that one myself, I only have Lone Echo via the store and it's not actually running on Oculus hardware so I'm still using PiTool + SVR settings for it.
I always do things like turn off PiHome, SVR Home etc to not run any unnecessary VR utilities chewing up resource without a benefit. And I only run FPSVR when I actually need to check the FPS, otherwise monitoring is introducing its own latency

Glad I don't run WMR Home any more, that was a hog afaik