I've had covid three times now and have a pretty good handle on my before/after fitness because I do (did) a lot of running and am geeky with heart rate date. Weirdly I've found in my case, the milder the illness the longer the recovery. Last covid was in September 22 and I'm still shattered all the time with resting heart rate alarmingly high.
I do worry that in some senses a 'long covid' diagnosis is essentially the medical profession shrugging it's shoulders and giving up - it's not like the Dr is going to give me a course of tablets that will sort it out. I am getting tested for other stuff now as well though.