I can no longer recall the exact quote of kasparov. But it's related with studying a lot of master games.
It really depends on the students/amateurs . There are are amateurs who enjoy/get pleasure studying chess a lot. There are amateurs who don't enjoy it. If a player only seeks entertainment then he can just simply play without studying that much. If a player wants to get better but don't enjoy chess training, he should get another hobby/field(kasparov has a quote about this too, I just have forgotten where I saw it).
International Master Silman was quoted saying he quited chess because he can't take the rigorous process to be a GM.
Also, I think it depends on what level you are currently at. If you're under 1800, it's essentially due to poor tactics. Looking at the games of players with those ratings you see the advantage swing back and forth at least several times during a game.
I'm not doubting you, but when and where is Kasparov quoted as saying that? It's just a bit surprising. Maybe he was trying to plug his books.
I remember Kasparov saying the importance of studying many master games. Actually it's not only kasparov that says this. Majority of masters advices novice to study a lot of masters games.
I think there is no harm if a below 1800 study strategies. Of course the novice needs to improve his/her tactics. But there is no harm studying strategies. Studying strategy will help a novice get good positions. Of course it can be ruined by a blunder(this is where studying tactics comes in, to help you getting better at winning good positions). Studying strategy will give novice a clue what to do if he can't find tactics. Chess can become boring too for novice if they can't see a tactic, and are clueless on what to do.
If a novice gets a good position, he can still lose by blunder against a fellow novice. But if we will go for percentage/stats, I will guess that most novice that gets good position probably will win 65% of their games against a fellow novice opponents.
Novice loses games because of poor tactics. But you can also see that they have poor piece placement.
I know a kid who always has an even score with his fellow novice opponents. Then one day I showed him a book that teaches basic chess piece placement/guides like castling, endgames,rooks are good at open files, trade when ahead etc. After reading some of this concepts this kid beat most of the time his fellow novice opponents.