Great analogy. A puzzle with 10,000 pieces of the same shape would be challenging. It also would be marketed to only a slice of the puzzle market.
CMBO was revolutionary in its "realism" step change, and hooked me. CMBB and CMAK being evolutionary fixed some of things I didn't like about CMBO but also introduced some new things I didn't like.
My expectation of CMX2 is that it will be revolutionary relative to CMBO. I look forward to it.
In the limit, though, there is a lot about war that is waiting, boring and frustrating even amidst a heated battle. This speaks to some amount of diminishing returns in "fun" relative to "realism." I trust the designers to find the balance, this being a very subjective thing (recall the 10k puzzle).
I think adding a "soul," as Steve characterized it previously, would offset the diminishing returns in Fun I experienced between CMBO and CMBB (never bought CMAK).