I am an achievement hunter on FFXIV, but I honestly only go after them to do something in the game while socializing with my friends. (This character is an alt btw.) I personally feel like the number does not matter; but the number could be a pretty good indicator to tell which players are extremely active, veterans, or new. I actually love going on the achievement page on my lodestone because its all listed in order and shows me what my journey has been like with all of the dates. I am like "huh... I chose warrior as my starter job 3 years ago. What a nice memory."

I do think having a number in the AD plate would be the best place to display it because you can't see anyone's achievement scores in the game. I however don't mind if it gets in or not.