As I remember it, the guy who wrote RCI won one major tournament, wrote his book, and then disappeared. And while he was a strong amateur, he never did obtain any level of title.
I think he did have a positive impact on the game of chess with his controversial book, in that it really put the emphasis on tactics, and especially for those who good benefit most from tactical improvement.
But he went too far. Tactics, while probably the one element that will make the most impact for those of us who are class players, its still not the whole story. After all, what do you do when you find yourself playing through an opening (which you know nothing about because RCI states opening theory is a waste of time) which has no tactics? Most likely come out with an inferior position and then its an uphill battle.
But say you come out of the opening equal or only slightly worse, but again there are no tactics - what then?
In any case, I think it will generate a lot of rating points, but sooner or later you're going to hit a ceiling because your opponents know tactics too, but they also have the opening and positional understanding that the one dimensional RCI player doesn't.
Me I prefer to study all aspects of the game, and I do study tactics daily as well. They're vital, and right now they're where I put the bulk of my study as I know they'll deliver results fastest. But I still study positional play, a little opening theory, and some endgame material as well - because I don't want to be a one dimensional player.
15 months ago, i heard all of the useless advice. then, i was rated 1300 icc rating. study endgames, study this or that positional book, read annotated games. i was excited, so i studied my butt off. so i returned with lots of chess knowledge. i even took lessons fron well known coah. i wasted lots of money buying a whole libary with books that helped everyone else but me. i had all this new chess knowledge. i got my butt kicked still. then came my glory moment , the day i search and search and found the well known book called RAPID CHESS IMPROVEMENT!!!!! i did the 7 circles suggested with only 2 tactic books and today my rating is 1707 icc. icc stands for internet chess club. so tactics, tactics, and tactics will give you the most bang for your bucks in the shortest time all the way to Expert. dont get me wrong, studying other areas is ok if thats what you like, but all games in the class level are decided by tactics. studying those areas will only hinder your improvement. i bet you that anyone that's studying other areas besides tactics, and they are rated below 2000 uscf , i bet you its been hard for them to see the improvement they think they shoud have even though they have gained more KNOWLEDGE. go ahead and read your 201 book and lose to the guy that is better tactically!
I don't believe all you need is tactics.
I've been steadily improving essentially non stop. I do a bit of tactics but I also study endgame and opening theory along with watching videos/reading articles on different topics and playing games to practice.
I believe positional understanding has a bigger effect in your games the higher you get as well. So where you may be great at tactics you can end up in games at higher levels where you can't make any tactics because your position isn't in as good of shape as your opponents.
I don't think anyone should study only one aspect of the game to make themselves a good player.