I agree, that's what I said "if what your parent comment suggests is true"
In fact, said parent comment said "It might have been a mere speculation but it kind of makes sense"
I agree with you that there is no predictive power in explaining things that way (indeed, what I said is speculation, hence why I worded it in the conditional), but that was not what I was responding to. I was only responding to the "design" part of your comment.
That being said, evolution does make predictions which have been confirmed. Notably Darwin's long-nosed moth. Here's a list of more predictions[1]
Well, I would argue that the vibe of your whole comment was coherent in that sense: you talked about what nature wanted, about design and about what kind of stuff would make sense while looking at it from a architect perspective.
It's a very odd way to look at it if you have no creationist conception of it all to be honest.
As for your point that not everything has an evolutionary advantage, I agree. Deafness and blindness exist after all.
But I don't really see your point as far as proposing hypotheses to account for certain prevalent traits, which, in my opinion, is what the original content was about (the grandmother hypothesis).
Put it another way, if I asked you "would you think that evolution would select for women bearing children until their 40s, or until they died?", you wouldn't be able to answer, because there's no predictive power in the explanation. Contrast this with "the sun rises every day because the earth revolves around itself", which allows you to predict whether the sun will rise or not tomorrow.