I can use Google, and found this [1] article claiming over 4 million DAUs for Calm in June of 2020, with trendlines going up and to the right.
So the lower bound of your estimate gives us ~200,000 people who would be adversely affected. Looking through negative reviews, it's all complaints about pricing and paywalls. The same is true for Headspace, the second biggest app in this space (I don't have DAUs for them, but it's got about half as many downloads and reviews, so let's assume less than half as big).
I can't find a single complaint about adverse mental health effects, which doesn't mean it never happens, but it's not anywhere close to 5%.
[1] https://blog.apptopia.com/calm-app-outperforms-headspace-dur...