Couldn't agree more on your hypothesis that - "covid attacks people wherever they’re weakest" - and in the case of Long Covid hangs around for months - years giving them more agony / pain than they ever had with their original problem.

If they had diabetes but no neuropathy - Their Long Covid immune system will introduce them to neuropathy.

If they had orthopedic problems - their long covid will make those joint pains hurt more than ever before.

Slight gastric problems become debilitating life changers with everything in your gut knocking you to your knees. Cramps, diarrhea, acid reflux, gas, constipation, nausea .... If it can happen in your guts - it will flare up with long covid.

Fatigue, headaches, nerve pains, exhaustion, Tennis, dizziness .... Yes - if you had it before, it will come back 10X worse.
I just don't know why it is such a mystery. With all the similar symptoms - don't we know what key organs are at risk and don't we have the technology to check them to see if they are being damaged? Don't we have treatment, medicine or test to examine the sympthoms and provide even the minuscule level of care. I'm not looking for opioids' for pain just maybe a probiotic targeted for covid or an anti-inflammatory for joint pain or something as simple as apply heat or cold - anything from a medical professional other than that blank stare.