yureesystem is not the only case of player that got strong focusing on tactics. Seems like a very good strategy.
I face 1500s and 1600s in this site and only in 1 out of 10 games, when I put the game on the engine, it looks like a "positional" win with the graphic slowly increasing on the winner side
9 out of 10 there's often 2 or more blunders from each side that drasticly changes the evaluation.
I don't know how much that counts between 1800s but until 1600, without a doubt, almost everygame is decided on tactics alone.
I've found my opening knowledge to be of great value even though i'm only 1500. I have trap lines memorized that people fall into more often than you would think and on top of that it allows me to get significantly better positions out of the opening. So I would say other stuff is probably more important to study, but in my case at least, studying openings has had nice results for me.