The source you cite has the following headline: "More than half of COVID-19 patients experience ongoing fatigue, study finds"

So I'm not sure why that article gives you the impression that any more than 2% is implausible.

When I see a medical journal article with n~150 saying that 50% experience fatigue after ~70 days, and an app reports that self-reported "symptoms" (may not be asking about fatigue?) are below 2% after 90 days, my takeaway is that much more data is needed because it could be that "a lot of people have long-lasting side-effects".

Think about if you (or a young healthy family member) tested positive and felt mostly fine for a week or two.

After reading both of the above, I'd be concerned that there's a decent chance (1%-60%?) that you'd be worse off in some way for a long time, possibly the rest of your life.