If that were true, I wouldn't said the Cowboy Bebop dub is way better then a lot of pre-lay cartoons.
But its fun to debate such things, clearly its an opinion based question, but opinions can clash and you can argue about the basis of said opinion or the premise the opinion is based on. There is no reason to get upset.
Pool size and money has a lot to do with how good a voice cast is, most people think the Disney dubs of the Ghibi films are some of dubs ever, because Disney has more money the dubbing studio and they can hire as many actors they want and they do have rely on one take.
as for your idea thaty dub actors have more to do with the materials they are given, I again disagree, because just because something is aimed at an older audience doesn't make it better, there are plenty of animes at that aimed at an older audience that are stupid, shallow, explotively, poorly written and rely too much on sex and violence (just like there plenty of good ones). I would rather watch something done well for kiRAB then done poorly for adults, I would rather watch Super frienRAB eps then the Eiken Club. Also the writing on Avatar is about a 100 times better then the writing on Naruto.