GMs and IMs might hate Micheal De La Maza but he was one of the few low rated player to go to expert level studying tactics only; that should be endorsement enough to prove that tactical studying is so essential to one growth as a player.
Michael de la Maza played sometimes 3 or 4 OTB tournies per month for two years. I suspect that this may have had something to do with the improvement he saw.
One of the reasons he gets criticized is he burned out, and quit playing in 2001. At least most of our GM and IM friends are still around, playing, teaching, writing books.
The main reason I use Micheal De La Maza is he did arrive to expert level tactics only; I look at some of his games and they are lacking some positional understanding. Micheal is good example a player with no talent and very low rating he studying tactics only and with hard work became expert level. He probably knew if he kept playing he probably will drop to 1900 and that is why he quit.
2 guys i know, study pretty much nothing but tactics. They are both Expert level players. And as soon as they get paired against anyone 2200+ they get destroyed.
I going with my experiences, I played a very 2300 uscf and outplay him in the opening and in the early middlegame I had a plus and slowing he started to outplay me and steer it to a rook and pawn endgame; he had a king, king rook pawn and king bishop pawn and rook and I had a rook and king and miss many draws chances and lost. So opening doesn't matter against masters because they are stronger in tactics, know their attack patterns and some them are beast in the endgame; so if you want to be successful get better in tactics and endgame.
Some expert achieve 2200 uscf and drop back to 2100; why?, tactics and endgame skill are low par against masters.