... A certified FIDE trainer in my chess club teaches kids only endgames the first months.
Endgames are even more vital for kids.Kids learn how to move the pieces with very few pieces on the board.Then the first checkmates(K+Q VS K ,K+R VS K etc.) is their introduction to planning , thinking and calculating.
Then the basic endgame positions follow then ...
Didn't you tell us that, while lacking an understanding of the value of endgames, you went very fast to around 1500 FIDE (in a matter of months) by studying mainly openings?
I am living proof that the NM level can be reached without focusing more on endings than the other 2 phases of the game . I have focused the bulk of my chess study time on middlegames and openings with the least amount of time going to endings and this has resulted in the ending being my weakness when compared to the other two phases , most of my wins come in the middlegame and I try to play my games in such a way that a crisis is reached in the middlegame because at my age I no longer have the stamina/energy to play long drawn out endings anyway ...