Just a comment on the following:
With a hard cap, the queue of transactions can only clear at a specific rate. Below this rate there is no fee tension, and above it there is instability.
I don't think you can say that - that would be like saying, queues are never a problem as long as utilization is < 1 (which of course is required for stability). But long queues do in fact develop when utilization is < 1, due to variability in service / arrival times (re: bitcoin, the dominant source of variability is in inter-block times).
As long as there are queues, fee tension will be present, as mempool transactions are largely prioritised by feerate. Empirically, we are observing periods of fee tension (i.e. busy periods, when pools' max block size is reached) quite often these days.
Otherwise I like this perspective on the block size problem (even though I can't really comment on the proposed solution), in particular the observation that in the short term transaction demand is inelastic. (Upon further thought, however, proponents of increasing block size would say that the inelastic demand problem doesn't really apply if the block size cap is sufficiently higher than the average transaction rate.)