I'm sorry, but anyone who doesn't hear the fundamental difference between Epica and NW/WT probably heard one of those bands only from the windows of a passing car. If "female vocalist + usage of orchestra + generally can be classified as metal" (doesn't that describe uneXpect as well?) is enough to accuse any of them to be copycats, then I guess we can throw away most of metal, because despite all the subgenres, it's all derivative af.
And while I like (well, liked, I'm not so sure nowadays) Nightwish, Epica (and it's spiritual predecessor After Forever) is infinitely more interesting music-wise. Even the "epic" NW songs is still mostly some random pop melodies (which keep repeating as their career gets longer) stacked together, with Epica I'm much more at ease calling their results actual compositions, with at least some untrivial approaches. Doesn't mean you have to like it, but it's really a very different beast.
Also, Epica has an actual guitarist.