I don't object to your opinion that Hide should not have a movement penalty--it's a fine opinion to have. But "to make it more like other MMOs" is rarely a good enough reason to change something about the game.

If I were to argue for eliminating the speed penalty for Hide, I would bring up two things.
  1. Gatherers no longer have a speed penalty on their stealth.
  2. The number of situations that Hide allows you to sneak through content in any sort of meaningful way is incredibly rare. The last noteworthy use of Hide that I can think of is Final Coil Turn 1 (T10) where we used to have NINs sneak through the stage until they unlocked the boss shortcut for the whole party. That makes it about six years since Hide's stealth effect was game changing. The benefits of Hide as a stealth ability being almost non-existent, it doesn't need a penalty attached to it in PvE.