it merely makes you spend 2 more builders than before.....Had the check been extended greatly such that you somehow stay fully in brick-by-brick mode in order to brute-force through a thin ceiling once builder gets close enough to it, then at least one can more convincingly argue "prevention". Instead, right now you just get a halfhearted bit of extra resistance towards the end.
2 builders is a lot and I wouldn't call this halfhearted at all. 2 builders is quite a large investement in Lemmings and in the most cases it is more than enough. + These 2 builders are still succesful in removing the weird feeling of "suddlenly it connects" from the genesis case.
It won't prevent the 20 of everything levels to do this, but it will in nearly all cases prevent the restricted puzzles from having backroutes using this behavior.
Even Simon found the NeoLemmix behavior initially confusing and surprising, not the Genesis version
The other way around now: I found the Genesis bahavior very confusing and I think that extra resistance is needed there. And that is also not just initially feeling so, but even after a time-period knowing about this.
Additionally Simon also admitted that my feeling about that the builder connect in the previously mentioned Lix level felt confusing and surprising to me is understandable as well. So this goes both ways.
no other Lemmings-like game checks like this
I think the old games got it wrong then, but I must emphasise here that I don't think the old games are a good reference for physics at all as they are riddled with glitches. Also quite a few checks are different from any other version now anyway due to removing old bugs/glitches and inconsistancies.
Let me give you an example why the gap between the 2 checkboxes are a very good compromise between the weird genesis behavior and a very strict large checkbox without interruption:
Imagine you are building up to the first floor in "King of the castle" from the bottom left. You started a little bit too late for the strict check and stop quite a bit below the ledge. With the 2 seperated checkboxes it will still end you up close to the ledge and it is possible to recover because of the little bit of leeway you have and the feet-check still prevents the way-too late attempts. So it provides a bit of extra leeway here and avoids frustration when building towards a rough-edged (but still more or less vertical) wall as namida stated.
So I would call namida's instinct to be correct here as it provides a compromise between weird genesis ceiling connections and the way too strict brick-by-brick mode.
Yes it takes a bit to adjust coming from the old games, but I think it is for the better as I agree with namida's instinct here and I would even lean more to the stricter side than the genesis side.