Comment is absolutely הערה, and response is תגובה, except in the sense of a "comment" on a forum, a Facebook post and so forth. For some reason we translate "comment" as תגובה in that context.
l ביקורת for comment? It works in some specific contexts. My English is not "native" enough to be sure about this, but I think you publish an article that is a "comment" on someone else's article, and in Hebrew it would be more ביקורת than הערה.
Is the placing of the article "a" correct in the english translation? Duo gives the correct translation to be: He has too long a comment. Wouldn't it be better with: He has a too long comment. Or even better: His comment is too long.
You would never hear a native English speaker say "he has a too long comment". You could hear "his comment is too long", but the Hebrew translation of that would be "התגובה שלו הוא ארוכה מדי", (although I am not sure if the "הוא" is absolutely necessary).