I'm not sure if what world Anthony lives in, or if he has never played a proper otb game with classical time controll. But I rarelly see gambits played against the French, the open Sicilian is very common and it's not at all uncommon to see 2. c4 against the dutch, but maybe that's just my club experience, and it doesn't reflect the rest of the chess world.
At what level do you HAVE to study book moves?

I'm not sure if what world Anthony lives in, or if he has never played a proper otb game with classical time controll. But I rarelly see gambits played against the French, the open Sicilian is very common and it's not at all uncommon to see 2. c4 against the dutch, but maybe that's just my club experience, and it doesn't reflect the rest of the chess world.
I agree. Plenty of players under 2000, including myself, play mainline openings and spend a lot of time studying theory. I do believe, however, that you can get to a rating of 2200 or so with tactical, middlegame and endgame skill alone, as long as you have a good grasp of opening principles.

At my level, all I see are Accelerated Dragons, Ruy Lopez, and Stonewall games. In fact, I am one of the few players who still plays 1.e4 e5

I'm not sure if what world Anthony lives in, or if he has never played a proper otb game with classical time controll. But I rarelly see gambits played against the French, the open Sicilian is very common and it's not at all uncommon to see 2. c4 against the dutch, but maybe that's just my club experience, and it doesn't reflect the rest of the chess world.
No, same here.
Generally I'd say people getting past 1600 are booking up somewhat.

I also know an IM who says he got to ~2100 just by being good at tactics. My typical answer is that you shouldn't look for outliers such as this. This IM might eventually be rated 2600+, which not many people get to.
I think it might be better looked at as how much a handicap you get from not studying book openings.
Take two parallel universes. This guy studies book openings in one, doesn't in the other. Other aspects of study are the same. I think he'd have gotten better quicker if he had done it. (But it would be an interesting discussion).
The 500 pt rating difference is interesting though.
I think that for a typical person, you can get by pretty easily not knowing book openings. There will be the occasional game where you lose very quickly, and where your opponent really put 0 thought into the game. But if you play more simply, you can probably avoid that stuff.
I say a handicap of about 300 pts would be my guess.

I also know an IM who says he got to ~2100 just by being good at tactics. My typical answer is that you shouldn't look for outliers such as this. This IM might eventually be rated 2600+, which not many people get to.
I think it might be better looked at as how much a handicap you get from not studying book openings.
Take two parallel universes. This guy studies book openings in one, doesn't in the other. Other aspects of study are the same. I think he'd have gotten better quicker if he had done it. (But it would be an interesting discussion).
The 500 pt rating difference is interesting though.
I think that for a typical person, you can get by pretty easily not knowing book openings. There will be the occasional game where you lose very quickly, and where your opponent really put 0 thought into the game. But if you play more simply, you can probably avoid that stuff.
I say a handicap of about 300 pts would be my guess.
A master at my club said his performance is like 500 points worse if he is playing an opening that he doesn't know compared to one that he does.

The beauty of modern engines is that you can research your favourite opening systems and check certain continuations that appear feasible, but are not played at high level OTB, so your opponent is unlikely to find it in a database and is thrown onto his or her own resources. In the old days of the Soviet Chess School, this used to take a group of GMs sitting around smoking endless cigarettes and debating lines. Nowadays you can do it at home yourself.
Hehe. This is so true. Technology rocks.

I say a handicap of about 300 pts would be my guess.
I guess time control may contribute to this, to some degree. If you know/have prepared a line, then you can play it quickly without thinking. If you are just relying on tactics from the start, you have to spend time figuring out what you want to play. Assuming you instinctively play what are actually book moves up to, say, move 4-5, your opponent (knowing their theory) will reply quickly without loosing any time on their clock. This will leave you with a disadvantage later in the game. On the other hand, if you go way off-book early then you are both as lost as each other!
I'm not saying this accounts for the whole 300 point rating difference, but it must contribute a bit (particularly at higher levels).
I'm interested to know how high an otb rating people think a player who understands opening principles but doesn't EVER study theory/memorize book moves could achieve? My guess would be around 1600 (not that I have any idea at all). On the other hand, I've read an interview with an IM who said he never studied openings until he reached 2200 (but I don't know what he meant by "never").
Obviously the question depends on the ability of the player, but I'm looking for a guess at an average - an idea of what level it becomes essential to study openings.