I would agree the "don't blunder" and "punish opponents blunders" are harder than endgame knowledge. However, knowing the basics of endgames is actually importa

I would agree the "don't blunder" and "punish opponents blunders" are harder than endgame knowledge. However, knowing the basics of endgames is actually important to closing out games. Specifically, knowing KQvK, KRvK, and the "ladder technique" is important. Without any tactics "take free pieces" probably only gets you to around 1200 (chess.com), but if it includes knight and pawn forks, skewers, pins, and discovered attacks it can get you to 1500. Playing perfectly every game is hard though. I would recommend having more chess knowledge than just those 3 rules before you really try for 1500.