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True, but isn't 'intuitiveness' all about catering to human peculiarities?

I think here it depends strongly on which humans and in which context; after all most multi‐leg movers with slider components do have the option of zero‐length stages — GraTiA's gryphon/anchorite and Mideast/Rennchess' duke/cavalier are very much the exception afaik, so from a design (and usage) perspective the 0‐step leg option seems to be the more intuitive. The case with reading descriptions is slightly different, because you have to say both stages of the move and consciously we count starting from 1 (unless we're mathematicians or programmers), so it often requires being explicit in the verbal description.

[…] that in all kind of other cases people will get extra moves because they did not count on a slider leg also eliminating itself by taking 0 steps.

Oþoh I can see the other case where someone expects to simply be able to write e.g. [B-fW] for a transcendental prelate/contramanticore, and is confused by the fact that it disallows the W squares; ofc in this case it's simple to add them by hand (the ? notation doesn't handle this case) but with more complex moves it may not be. Whereas imo in the opposite case, where the contramanticore has to make at least a knight's move, it's likely to be more readliy apparent that an extra F step is needed at the beginning to force that (or indeed two or three extra such steps if necessary). And surely it's more intuitive to specify three initial W steps (after the F one ofc) for the Tamerlane giraffe (“one diagonal and then after that at least three straight”) than only two?

Reminds me a bit of regexps; the Kleene star * there does explicitly specify 0 or more and if you want a minimum n^r of repetitions you have to specify them explicitly (or use syntax extensions like +)