Which prep company said this, out of curiosity?
There are really two separate issues -- how hard the questions are on the test, and how hard the 'grading' is. Twenty years ago, the questions were mostly fairly easy, but you had to get almost everything right to get a good score. Ten years ago, the questions were often very hard, but you could get a good score with many wrong answers. The more recent test would feel harder, but your score would be the same regardless of which test you took. It's really impossible to tell without a lot of data how 'hard' the test is these days, but my impression is that the questions are often a bit easier than they were ten years ago (which means you have less latitude to make mistakes). But your score has to be the same no matter how hard the questions are, because GMAT scores need to be comparable across eras, and they can't 'grade' people more harshly now than they did three or five years ago.
I have no idea what someone could even mean if they say the test was "twice as difficult" as it used to be.