Earlier quoted context omitted.
I don't think the issue is being professional or not. If the author's goal is to convince people who work on Hugo to improve the docs, then it's best to avoid triggering a defensive emotional reaction. The title as it stands will likely trigger hurt feelings, which is usually followed by being defensive or ignoring the substance of the criticism. That's simply unproductive.
The only thing I agree here is that better language wouldn't hurt. I don't think most people get "triggered". That's a vocal minority perpetuating a culture demanding a sort of conformity against their definition of "micro-aggressions" and "triggers" with no regards to a larger consultation with the society.
Saying "your project sucks" or "your project docs suck" is not a _micro_-aggression, it's a macro-aggression, or as I prefer, being a jerk. I think most people would react negatively to that sort of statement.