I agree with most of what you say, but I'm actually more surprised that DW got pusblished in the first place. I thought back then that even SC wouldn't sell that well. Sonalysts really should be given credit for their decision to make either game.
That said, I am a bit bored as well of yet another WW2 subsim. It surely won't be bad, but it's just more of the same. Doesn't lose that "been there - done that" feeling to me. Again a company chooses to play it safe by releasing yet another sequel. The SH5 forum is full of people who even now promise to buy it at its day of release or pre-order it
Though it's good for the devs, it just rewards Ubi's unimaginative product policy.
What I'd really love to see would be something like 'Red Storm Rising' (I know that there's currently a project underway to make it work on modern PCs). I mean a Cold War subsim (and I really mean: Cold War, not some 'fight terrorists / pirates' on a submarine, and no other slightly weird political scenarios we had in DW or SC). It doesn't nearly have to be as detailed like DW, but I'd rather like something like a Command-style subsim in said era, and it really should appeal to new players. Apart from that, I'd guess that Dr. Sid's Comsubsim is still years away from being really playable. Regarding the development costs of games these days, I wouldn't expect a company to release anything like that in the near future.