No, they're not using the same engine at all just because there are some functional similarities. That's not how this works. Yes, XIV takes some inspiration from WoW and there's nothing wrong with that if they copy the good things.
High numbers are cumbersome sure, that's why they're reducing them in the upcoming expansion, but I don't get your point - after you play the game for a while you can tell which values are low or high for damage etc., doesn't matter if it's 100 or 100k.
Remake of XI is not happening.