Btw, by 'Closed Main Line', I mean this:
Interesting but I feel like I struggle against
a4 isn't a problem when ...d6 has been played (which means that 8.a4, a very common Anti-Masrhall would be more worrisome). A very solid option is 9...Bd7.
why not learn the old steinitz? GM Dzindi released a two part video series on it here on chess.com. the lines take a different flavor with black often getting interesting asymmetrical positions and for a fraction of the theory required to play a normal ruy lopez.
actually i think after playing it for a bit you learn a lot of very subtle ideas involving pawn structures and positional chess. You see class players often dogmatically learn to fear double pawns and in the old steinitz, bb5, bxc6 bxc6 is quite common . blacks position is fine but you must learn to think dynamically, (how to use your bishop pair, how to use the open b file with rb8 or qb8, removing endgame pawn weaknessses with the a5-a4 pawn throw, when to keep the center compact and when to play d5 or c5). once you get past the initial "ugliness" of the position ,you actually begin to grow fond of the asymetrical fight it promises.
now some people may wonder? why play the old steinitz over the modern steinitz? i can think of 3 reasons
1. you want to avoid the exchange ruy. the exchange ruy is not common and not considered dangerous but it has its fanatics and just like letting white get an exchange french is often not pleasant despite equalizing, allowing an exchange ruy can be undesirable.
2. it gives white a tempting d4, which allows, exd4 nxd4, bd7, followed by g6! which is a unique position. the newer steinitz doesnt allow d4?! due to a well known trap.
3. the old steinitz gives white a false sense of security because lets be honest, its often most seen at the amateur level where they rather defend the e pawn right away then learn opening theory. a similar underestimation that you see of the philidor defense. This is especially advantageous agaisnt overly agressive and impatient players
The Ruy Lopez has been around almost as long as Chess but has been popular & subject to extensive analysis for the last 150 years. I started with it because it is very good for learning opening principles but eventually I switched to the Sicilian (usually the Dragon) to avoid all my opponents preprepared lines. So to me the question is, do I want to prepare for an opening with so many lines & variations all analysed out to about 20 moves or avoid it by playing something else. I chose to switch to the Sicilian & have never looked back.
Interesting that you say that, because I thought the Sicilian was supposed to be more theory heavy than 1.e4 e5. I tried switching to the Najdorf a while back and I played some games over the course of a few weeks, but I went back to 1..e5 when I realized how much theory there was to learn and how badly things can go wrong if you screw up!
e5 is more tactical, c5 is more positional.
Positional lines are less forcing, and the number of variations branches out more rapidly. Tactical lines are more forcing, and the theory tends to go deeper.
In a positional opening it's harder to comprehensively learn the moves out to a certain depth, because there will be more to learn.
But it's often easier in positional openings to find viable moves that get you out of the main lines. They also tend to be less sharp.
In a tactical opening it's easier to comprehensively learn the moves out to a certain depth. But it is harder to find viable moves that get you out of the main lines. They also tend to be sharper.
So you could say there's more total theory to learn in a positional opening (i.e. 1... c5), but it's also more okay if you don't know it, and it's easier to get out of it. In a tactical opening (1... e5) there's less total theory but you have to know it otherwise you may just lose.
Now, with modern engines you can develop rehearsed lines, i.e. theory for any opening.
However, some openings are alot more common than others. The Ruy Lopez is one of the most common openings in chess. In these openings... regardless of whether they're positional or tactical the theory of your opponent is going to be both broad and deep.
A very major part of what it actually means to minimize opening theory in practice is avoiding common openings and moves. So you look at a database and see how frequently a move is played, and consider how good of a move it is... if you can find a good move that's rare and fits your style then you're in business. It's easier to do this in positional openings, not so easy to do this in super-analyzed and tactical openings.
In the Ruy Lopez the morphy or berlin are played about 75% of the time... the Schliemann is played like 5% of the time, the Cozio is played like 3%, the Bird is played like 2%. If you want to "avoid theory" you could play one of those 3... You could also just avoid the Kings Knight setup entirely, since that's one of the most common setups in chess.
Also there are some of trickier / less common sicilians, like the four knights sicilian or the nimzowitsch sicilian. At that point you're completely out of your opponents theory in almost all cases pre-2000. I play both of these all the time and almost never get the main lines...
But it's not as straightforward as it seems to say one opening is theory intensive or another opening is not theory intensive.
Btw, by 'Closed Main Line', I mean this:
Interesting but I feel like I struggle against