it's better to study endgames first (beside tactics) because:
1. you learn the effectiveness and coordination of your pieces
2. you learn to calculate
3. you learn how important your pawns are and how to handle them
4. you can often score in games where your opponent is ahead, if you have better endgame knowledge
5. you learn how to play the middlegame in relation to specific endgame situations (where to put your pieces, which pieces to exchange)
6. you don't have to look for a winning combination the whole time and don't have to force the win (it often will end badly) because you can easily lead over to the endgame, simplify the position etc.
Doesn't it make mor sense to study openings, then middlegame and finally ending. If you make mistakes in th opening, you ar unlikely to have an equal middlegame and if you dont play th middlegame well then th ending will be lost no mattr how much you have practiced it.