The QM did not say I should stop. If anything his statement means growing a body will get increasingly cheap as the soul gem tries to build a new body and gains experience.
If that was the case they wouldn't care about collecting grief so much. They'd just abduct meguca after they made their wish to put them in customized power generators. There'd be no incentive for them to witch out.
Alright.
We are completely capable of lugging around their disembodied souls and preventing them from witching out.
But honestly? Aside from the moral implications of doing so, it's impractical. If we slip up, if we miss once, if we forget, if we sleep in - then they'll either successfully regenerate and escape, or witch out on us. Furthermore, if we keep them in gem-form, we can't interrogate them. With the time-stop, it was a friendly whom we were cleansing, and on top of that, she asked us for cleanses.
Heck, look at the section where we got hit by a mine - the amount of marbles we got from the healing was huge. Healing takes more energy then stopping time. Does it make sense? No. But it doesn't make sense for emotions to have a tangible effect on reality either - not as energy, certainly not as reality warping eldritch abominations based off the souls of the source of the emotions.
Furthermore we have no evidence that holding onto their soul gems while they continue to generate a body would in fact overwhelm our rate of grief bending in our sleep. In fact we know this isn't the case because in the PSP games you can see that the soul gem can be separated from the body for four DAYS without witching out. So them witching out during a sleep cycle isn't going to happen.
We gathered 100+ grief marbles when Homura and Mami were working together to heal our leg. They're trying to do a whole body, and it was noted that it took "past an hour" to heal a single leg. If we sleep a normal 8 hours... that's 800 marbles worth. Not to mention the psychological effects - complete sensory deprivation, combined with grief-spirals and (in Kirika's case, at least) the fact that they failed to protect their girlfriend? There is a lot of potential to go wrong there. (Also... are the PSP games even canon? )
It takes past an hour and several more cleanses to heal your leg fully- that mine had made an utter mess of your leg. Homura did the majority, though not by much, of the work, her healing seemingly far more efficient than Mami's, who simply brute forced it. You speculate that perhaps Homura simply had more time to hone her skills.
There is quite a bit of dissonance with Sabrina's leg being utterly mulched, and her blithely talking about other things as if she doesn't care.
You now have a hundred seventeen Grief marbles, twelve of which are in your pocket.
Homura, who is super efficient and experienced, would generate much less grief then Oriko and Kirika.
