Legitimate concerns and something for me to think about... But if I am truly relaxed in all those areas, and not just squishing into a bag of bones of the floor, then something is holding me up.
So the movement organization of holding me up could be done in such a way as to deform me into those two middle diagrams I have above if I was holding the "wrong" way... Or it could, as you indicate, collapse me into a more ideal structure, but only if I have degrees of freedom in the right places and to the right extents by organizing structure in other places.
So still you get, where is that structure and what's it doing that allows those places to be relaxed and not actually need to carry the stress in the first place? I guess what I showed was an example of what I think is one such pathway, though here it is active rather than passive.
Well you always have to have structure. Without structure we can't get much of anything done, but you can have structure and be relaxed. That's the problem with a lot of aikido, people think getting relaxed means losing structure, so they end up feeling like cold fish, which requires the other person to also feel like a cold fish so that you can do techniques. Anyway, if you also tuck in your chin a little and really relax the hips/buttocks so that you can feel gravity pulling down on your lower spine, you help elongate the spine and naturally round it out, kind of like your last drawing though without it really appearing that wa, which only increases your structure's ability to send energy down rather than having it break your structure. It ain't easy and it takes a lot of practice and conditioning, and that's just the basic static version. The rabbit hole is horribly deep.