Every group that is successfully clearing the hardest content of every update is using ACT, or some other third party service, to measure DPS/HPS/Standing in fire/etc. It's essential information for a successful group in that content, and so a DPS meter is an essential tool.
I can't think of a single MMO, popular or not, that lived its life without any of its players using a DPS meter. It's as much a part of the MMO genre as anything else. FFXIV is one of, if not the, most modern MMO; and it has the subscription count to cement it as a very big MMO title; and yet, it lacks a mandatory tool for endgame.
Most of all, showing all players a way to measure their effectiveness in a group is very good for the game. Imagine the difference in competence between someone who leveled 1-60 oblivious to the idea of a parse vs someone who leveled 1-60 and monitored their parses the whole time. It creates a huge gap in the basic knowledge of playing well vs playing poorly.