This isn't really specific to COVID though, any serious illness can do a real number on you.
Anecdote: I'm an avid runner and cyclist, but after I had dengue fever, it took me months to regain my fitness. I used to run 10K's before breakfast, but the first time I attempted a 5 km walk afterwards, I was basically comatose for the rest of the day.
I was never an avid runner, but I would jog in the morning sometimes. It was supposed to be a habit, but never was.
I noticed a huge difference in performance before and after getting sick with Epstein Barr in 2017. Even years later I've never returned to the same performance. Maybe related, maybe not, but that's how it looks to me with my sample size of one.
When I got dengue I was really bad for a few days but quickly recovered and actually improved my fitness/health due to changing lifestyle (so it's biased). Wasn't it chikungunya?
Nope, confirmed with blood test. Dengue is quite weird though, it's asymptomatic for most people who get it, under a percent get hemorrhagic shock and end up in hospital, and the rest like me are anywhere in between.
Post-viral conditions happen, yeah, but the percentages coming out of long COVID studies as well as the sheer number of anecdotes everyone has seems fairly novel. At the very least, even if there's a similar prevalence of these issues for COVID, the sheer amount of infections is going to mean this is a larger concern for COVID than other viruses.
People talk about NEVER recovering their previous cardio performance after a COVID infection. No one expects anyone to be seriously sick, and then have anything resembling their previous performance levels when they first start back.
Anecdote: I'm an avid runner and cyclist, but after I had dengue fever, it took me months to regain my fitness. I used to run 10K's before breakfast, but the first time I attempted a 5 km walk afterwards, I was basically comatose for the rest of the day.