If we're comparing the basic default UI of the two games (no options or anything), then SWTOR isn't bad. I actually prefer their centralized setup of their player/target and main action bar. But obviously we can't make that comparison without noting that WoW allows customization of their UI, something SWTOR doesn't, and that's not including the additional options you get with mods.
I don't get how anybody would be against mods completely. I understand being against the more invasive mods like BossMods (which would essentially call out the boss fights for you) or Questhelper (which would stick an arrow on your screen, essentially telling you how to play), but a majority of the mods were "quality-of-life" mods that made playing the game much more enjoyable. In fact, a bunch of the features now adopted in WoW's default UI (and subsequently SWTOR's) were introduced by mods. Floating combat text? health/cast bars over friendlies/enemies? The grid-style raid UI? all mod inventions. The most attractive solution is to allow mods, but restrict those that alter the gameplay.
What probably worries me the most about their no-mod stance, is that they stated they have no intentions of putting in a threat-meter in the game. Threat mechanics always seemed like an essential part of the games and to some raid encounters. It brought an additional layer of complexity to end-game for both DPSers and tanks. Not putting one in this game, has me worried about the difficulty of the end-game. I wonder if the encounters are going to be simpler to account for this, or if tanking is going to be trivialized.
p.s. mouseover healing is desperately needed... i can't remember playing with any healer that didn't use some type of healing mod