He is a submariner, so he was thinking from pure mil perspective I guess and he really wanted surface and subsurface assets forward deployed.
I guess yes, UK is a bit constrained with resources seeing how the new programs are going. For the basing argument I think that it could be packaged nicely into the overall program, like we did with Kilos for the Black Sea.
3-4 submarines provide better coverage than 1-2 submarines, even if the two are more capable, particularly when selecting between the mixes.
Note how you have omitted the Arctic and how many of those areas would benefit from having in theatre submarines in general (recon and spec ops, threat of SLCMs etc) without them needing SSNs specifically.
A small number of them can be offloaded to UUVs though I guess.
p.s. are there tables for the RN technical readiness on the lines of Shishkin's work?