Not entirely true. There is some transfer of body shape, it just doesn't work how you think it should logically. [...]
Yeah, there are some limitations to that method you described. You are still bound to a bone matrix (tensor) operation as a diffence between Maker and Game char profiles. You can by far exeed the limits of the actual game transform matrix in the maker, but you will be "reduced" to the slider system ingame. I do not know how invasive your edits were, but since they showed up in your game, maybe you did some other tweaks as well (disabling body system morphs, maybe?)
To give you some direct thoughts on your described method, I followed your steps and made a profile for a High Elf. The Maker edit is by far exceeding the ingame bone matrix.
Since you said, there was a way to override the ingame morphs, maybe you have some luck breeding this preset, because I tried to get this, but the game was not willing to grant me any offspring with the actual preset - even after excessive breeding (about 50+ offsprings) to circumvent possible Random Number Generator flaws.