I guess it depends on what you consider a "decent amount". Within the overall context of whether text posts would be popular or not on TikTok, 5-10% of globally-trending posts being text-heavy seemed like a decent amount to me but YMMV.
But, you are right that I was talking about text posts in general rather than directly responding to the videos about reading text from reddit/twitter that this subthread was discussing though. I see those often but I don't see them currently trending.
I definitely used to get videos with walls of text that are obviously trying to game the algorithm by getting you to read an essay to increase watch time. Once I habitually scrolled away from them I stopped getting them. That isn't even related to the claim of voices reading screenshots of tweets or reddit comments.
I absolutely believe that videos exist where there are text-to-speech readings of tweets or reddit comments and that the commenter referencing them sees a decent amount of them in their own feed. But I do not believe they represent a "decent amount" of the majority of TikTok users feeds.