Yes, I appreciate those points, but I think movement related issues can be worked in their own way too.
Gains and merits will always be relative.
It's very easy to say "work your weaknesses", but it's not always apparent what they really are. They're not intrinsic, absolute, or discrete. The relevant weakness is the one that helps achieve the gain you're looking for, and it's very often not at the point where you're failing.
There's often substantial risk involved in estimating where the best investment needs to be made. In contrast, it can feel comforting to focus on where you're failing, but that can be defensive and impact negatively in the long run - the trying not to fail approach.
Of course, this thread is about considering the relative merits of the different strengths/weaknesses targeted at 50+ vs say 40. That's why the thread is actually quite interesting, isn't it.
I think it's misleading to try to argue for one focus over an other, as though one is ultimately right, the other wrong, but I think it's relevant to differentiate between skills and strengths. They're matters of interpretation too, but I think it's important to be wary of which lens we're looking through.
