I don't mean as in "you waste too much time on the opening stage" - perhaps I do actually - but I was recently thinking how studying theory could in part hold you back as a chess player (at the amateur level of course) since you don't think for yourself and don't develop any creative capacity for the opening.
I recently switched my repertoire up from the Caro Kann and Queens Indian as black (which while very good openings, aren't very sharp nor require much calculation at my level) to the more sharp Sicilian and Kings Indian to develop my calculating ability as I noticed the majority of the world champions played these openings when they were first starting out, and I felt held back by my previous openings. I mention this because the Sicilian and Kings Indian, by virtue of their sharpness, are extremely theoretical which in part I think can hold someone back when they first pick them from improving their calculation and tactical ability because you aren't really thinking for yourself and instead following what other's have recommended. This of course has a place and time, before a tournament you want to get all booked up to play with optimal advantage - but on a long-term basis, I think deciding what to play yourself in the openings and not thinking too much about theory can be beneficial to your skill and calculation.
I believe it was Capablanca who didn't study theory until he got to a very advanced level, and clearly he was fine, so I think avoiding learning theory until it is absolutely crucial that you do, could be more beneficial in the long term - assuming you still analyse your game afterwards and fix any mistakes and improve any moves.
I'm only 1800 Rapid so at my level there is not a lot of theory so I may just be preaching to the choir but I just wanted to share my thoughts on why theory is a scam :p
You are absolutely right: opening theory is a waste of time: high effort, low reward.
Capablanca did not study chess at all.
Study of endgames is much more efficient: low effort, high reward.
Don't forget to solve tactics as well!
If by learning theory you mean 'memorise lines to 20 moves depth without understanding them', then yes, its a complete waste of time.
If you mean 'learning the ideas and thematic moves of an opening', then absolutely you should do it.
e.g. in the Sicilian, the importance of d5 as a square White wants to control and Black wants to break with by playing a pawn there.
Also, I (personally) don't regard the KID as especially sharp or theoretical (at least up to quite a high level) . It's strategic, and Black's strategy is often to roll the kingside pawns down the board and mate White by move 30, but as long as you understand what Black's ideas are, and where the pieces tend to belong, you can play the position quite decently without having to remember a very precise move order.
It really depends.
I ardently believe that you can go a long way (until 2000 at least!) without studying opening theory and still be perfectly fine. You'll get perfectly playable positions by playing the opening on your own and often you'll even get superior positions if you pay good attention to tactics and have the better strategical understanding.
Okay, maybe in some rare cases you will be outplayed straight from the opening by an opponent who knows their opening really well and lose. But for one, you shouldn't be too afraid of losing every now and then (it's bound to happen no matter what). When you lose, try to learn something from it and move on to the next game. Secondly, opponents who really know theory are much rarer than most people seem to think. One anecdote: once in a post-game analysis I told my opponent (elo 1550) that after 1. d4 d5 2.c4 there were basically three good moves: 2... e6, 2...c6 and 2...dxc4. He looked at me quite impressed and said that I seemed to be a big opening expert.
Even when opponents have studied theory it won't last them very long. Since you're playing on your own you'll make some subtle strategical mistake and at that point they are out of theory. A grandmaster would be able to adequately punish that mistake just by using their own skills. My and your usual opponents will not.
Even if they gain a clear advantage from the opening there is still a whole game to be played and you're bound to get some chances at some point. No one converts perfectly.
I think a lot of lower-rated players like to study openings because a) the chess community portrays it as much more important than it really is and b) it can be done without putting a lot of effort if you just go through some lines and try to memorize them.
All that being said (in summary: studying theory is absolutely not necessary by any means) I think that it can still be a valid way (out of many) to improve provided you're not lazy and really try to derive a deeper understanding from it. Such as: trying to learn general things (typical tactical themes, positional plans, how to harmoniously develop your pieces) rather than concrete variations. Analyzing master games played in your opening and seeing how they implement the plans you know about. Always askig questions, trying to come up with your own moves in a theoretical position and analyzing why they do or don't work. Reducing the usage of engines or databases and always coming up with your own ideas and judgments. Playing as many games as you can in your lines, maybe asking a friend to play a specific variation against you (particularly those where you're unsure about something). Analyzing those games properly.
If you study like this then you can probably quite improve your overall chess by studying openings. I've grown to enjoy opening study (maybe a bit too much) but I definitely feel that it helps my positional understanding when I first learn about long-term plans and piece maneuvers in certain structures and then experiment with them in my games and see how they work out in praxis. Of course, practicing tactics and studying endgames separately is still very important.
Tl;dr: studying openings is by no means necessary but imo it's still possible at any level to learn and improve via opening study when done with proper effort and without neglecting to think on your own.
Capablanca's father was a big fan of chess and had a collection of chess books. How could he not learn chess or study at home. Regarding openings I notice most of those who believed opening study is not important stay below 1900 online for a long period of time.
The best way is to learn a little bit about everything. The most fun way is to learn a lot about what you find fun or interesting (although you'll still have to work at learning).
Something like:
Do tactic drills a little bit each day (solve puzzles).
Learn about strategy. I suggest reading a whole book.
Then endgames (another book)
Then play over an annotated game collection (another book)
Then openings (I like to use databases)
After that repeat the process. Each cycle will gain for you many 100s of points. Strategy, endgames, annotated games, openings. After you decide you will be playing an opening line, you can make it part of your drills. Maybe on day instead of tactics you get out a board and see if you remember your opening lines without any prompts.
Water can be detrimental. Does that make it bad or something to avoid?
I think below master, few can claim that they have lost a game because of a bad opening. You can get a theoretically bad position and be perfectly fine a few moves later. Once you move up the ladder and become a strong player, the competition gets fierce and you will need the small edge opening preparation provides for you. The higher you go the more important opening becomes. But that doesn't mean that one should leave the opening aspect completely unexplored. Some openings like the Najdorf require knowledge of theory to some level as the positions are hard to analyze over the board.
The aspect of the game that gives you the most reward is of course the endgame as a lot of players avoid it and prefer to dabble in the rather "fun" parts of chess.
@piscatorox My point is I think it would be beneficial for you to work out and discover those ideas yourself, which while might make it more difficult in the short term should help you in the long term, though learning theory accidently is pretty unavoidable unless you actively choose to not analyse your opening stages which itself is not a smart choice if you want to improve.