I disagree with this post. Obviously when you A/B test a solution with a button in plain sight, it’s going to win over a button hidden by a gesture. No argument about that.
However when designing an app you look at the desired flow and how to fulfill it in the best way possible. Deleting comments is clearly not the prime focus of Instagram (neither is reporting an image or switching on/off notifications for a specific post), so why promote this by having a dedicated button in plain sight?
UX is just as much about solving individual problems as it is looking at the bigger picture, and to me it seems the writer is just looking at an isolated problem here.