TD,
As usual, we mostly agree.
That said, CBM wrote of his ideal links in his book, and not about how it specifically came to be ideal, although, in context, I think he thought NGLA came pretty close.
It's always a mix, including PV, where Tilly brought his pre-existing design favorite of the great hazard to the job, and Crump used it.
And, I agree most of us take more ideas into a project than there are holes, i.e., more than 18 (or 27, or 36) and it is easy to overthink and try to combine them, messing up the works, LOL. It seems to me that we all think some ideas are better than others, so having some kind of hip pocket list of ideals helps narrow the ideas down a bit. I may be wrong of course, but I don't think waiting until on site is really suppressing excess ideas, but its hard to get inside someone else's head.
To me, that is the essence of my argument in favor of pre-thinking design concepts, and then applying them ONLY where applicable. For instance, I don't think a Redan on a back to front sloping site is a great idea, so I wouldn't use it. There are gray areas, of course. Even a Cape Hole, which I think is great downwind (increases hope and temptation) can be used in other winds, except, IMHO< when the prevailing wind forces an aim out over water, which is uncomfortable and temptation reducing. So, even faced with a perfect Cape Hole by land, with that crosswind, I might not use it, etc.
My guess is that you have certain preferences that you look for when you reach a site (or do a routing on plan) and that you like to vary the details any time you use those preferences on a project to make it unique to the site, and more importantly, the best possible fit to the site.
But, it does raise the question of whether "all ideas are as valid as others" which I don't think is true. In your comments, it seems you want to reserve that judgement until the last possible moment, whereas I have, over the years, tried and/or not, and dismissed ideas that just don't seem likely to yield any benefit, no matter what the site says. Sort of like my opinion of chocolate sauce on roast beef....I feel no need to try that one out in the real world!