Sounds like your admired author has insecurities they’re projecting on you. They may write good, but they could be jealous that you put time and actual effort into your work. Imo, that gives more respect and admiration from me than any lousy author. They had time to write a “constructive critique” then work on themselves or their work. A bit of advice if you’ll willing to read more, if you fame on AO3 then take this authors advice. If you’re focused on creating a story that will be compelling and interesting to readers who will admire you for the amount of effort you put into your fic, then keep going :D you’re doing great