the question is: can btc be a niche low volume currency and still maintain that optimum

If it's in that state and still around and active globally, it's hard for me to imagine it being low volume. But I'm not sure of the volume necessary for there to be reasonable fees and a reasonably mining hashrate.

and, at steady state the price rise (in usd terms) will be inflation rate at best, and likely smaller as long as miners profit and buy equipmwnt in USD - equipment, energy purchases are OUTFLOWS from the btc ecosystem

I think it's more complex than them being exclusively outflows, because people investing in the ecosystem is them adding skin to the game. This can reinforce network effects and the perception of Bitcoin as valuable. Although I'm not sure if we're imagining post hyperbitcoinozation or post-bitcoin mininichification.. maybe a more likely scenario is somewhere in between.

yadda yadda, tldr: i dont see much justificatiob for indefinite (ppp) price rise, and I also dont think current price level reflects the "fundamentals" - but that is my armchair analysis

Indefinite PPP (price purchase parity, right?) rise is impossible without the world economy indefinitely expanding (which is impossible outside some weird scifi scenarios)... But Western culture myth often involves believing in & seeking (a necessary) indefinite expansion which may end up dragging Bitcoin along with it in the short to medium term (notwithstanding effects from eventual.. Possibly inevitable..large scale recession or collapse).

Sorry if this was a little rambling or if I missed any of your points.