It may be true that a huge chunk of the character's moves aren't going to be used regularly, or rarely ever used at all, but you need to be fully aware of them so that you know how you can punish your opponent if they try and use it. Plus you need to factor in which moves to use as general pokes, which to use in juggles, which to use if your opponent is against the wall etc. And when you have over 50 unique fighting styles, each with 100+ moves on average... that's a lot of shit to learn.
Now, I dearly, dearly love the Tekken series, and I probably always will. But then, I've grown up with it. I've played every console Tekken game, and sort of 'evolved' at the same pace as the series itself. So for me, the huge move lists aren't as much of a problem. But for someone who's only just got into the series, it will almost certainly be extremely overwhelming. To put it bluntly, the Tekken series from Tekken 5 onwards is not welcoming to newcomers in the slightest.
I think that's why they gave the new character Eliza such a stripped down move list - they're thinking of simplifying the characters down so that people will be able to learn them more easily.