Every chess player has to memorize opening theory or they can't make progress. I agree that this is often over-emphasized, generally because it's the easiest thing for a coach to assign. I do think opening theory is pretty fundamental because it is a constructive way to teach someone about controlling the center of the board and developing pieces, which need to be learned concurrently with tactics. The same errors that people fall into with over-emphasizing openings are also prone to occur when people over-emphasize solving chess puzzles or replaying GM games. If you spend too much time on any one aspect in the developmental stage, it's not good. But still, 1200 level players must really study a few basic openings just to even get a handle on engaging in a game of chess.

My preferred approach is to teach one or two main variations for a couple of openings for both black and white. Then, after these are reasonably understood, I like to spend time focusing on the goals of the opening, like controlling the center of the board and developing minor pieces to good posts. That's usually the point where tactics and combinations start to become relevant, so its natural to work on that. This is just my opinion, of course. I'm sure many chess instructors have their own opinions.

Playing slow chess is by far the most problematic issue. Chess requires so much patience, and thinking like a computer when your opponent is thinking about their own move is really hard, especially for children. Most kids don't have many options to practice other than internet chess, which is generally blitz dominated.

At any rate, I never believe that memorizing opening theory is an important goal unto itself, not even at the highest level. It goes in spurts. Maybe study the Ruy Lopez and Queen's Gambit to illustrate basic ideas about central control, then take a break from openings and play dozens of Ruy Lopez or Queen's Gambit games to build up the ability to systematically study positions and compute moves, then go back and extend some opening knowledge to study piece development, then play more games and study tactics and combinations.

My only point in my original comment was that because of the systematic approach to move calculation and focus of attention, top chess players are usually not concerned about distraction so much. It is exactly avoidance of distraction that they have been training for to get them into the big tournament games in the first place.