You can report people for harassing you about your damage numbers if they allude to the idea that they're using a parser. You can also check out https://ffxiv.consolegameswiki.com/wiki/Stone,_Sky,_Sea and work on your rotation if you aren't yet comfortable. In any case it's possible you were playing really poorly in which case I can understand where the tank is coming from but it sounds like he was being unreasonably rude.