... Give someone pawn odds in the opening, and it isn't worth much.
Give a 1200 rated player pawn odds in certain endgames, and they can beat Carlsen.
Mistakes with reduced material matter much more... although sure, if you're trying to play some sharp theoretical line, you can lose right away if you don't know what you're doing. The answer then, of course, is to not play sharp openings if you don't know what you're doing. You can play colle and london crap all the way to a title, the opening doesn't need to be a big deal unless you make it one.
Where is it advocated to make the opening "a big deal"? Is one going to learn about the colle, the london, or avoiding sharp openings by doing tactics drills?
IMO ideally you learn about lots of different openings, and the types of middlegames they lead to, by playing over a lot of GM games.
Unfortunately I didn't do this as a beginner because I wanted all the moves to make sense and I became frustrated. The moves don't need to make sense though. It's enough to just find one interesting thing about the game. It can be as simple as a tactic or maneuver. Also note general things like which side of the board the players played on (kingside, center, queenside) and in what way (pawns, pieces, both?)
Meanwhile the player is seeing lots of different openings, and will start to remember the moves to the most common openings as a consequence.
That would be my advice to a beginner.
you hardly ever get to play the lines you studied, for example i have played italian game 280 times online and reached the line i wanted giuoco piano 6.cxd4 Bb4+ 7.Bd2 only 17 times. focus on middlegame and endgame.