Well it's also possible to win despite sloppy endgame play due to having a significant advantage going into the endgame... and all games don't even reach an endgame. Again the argument is arbitrary.
A person sent this quote to me as a PM. It sums this issue up quite well:
"... the situations in which trainers work vary enormously. ... Some trainers work with large groups of students and others individually; with average low-category players or with bright and highly talented potential stars. ...
That is why I am skeptical about any attempt to introduce a rigid methodology, rigid rules telling us what to do and how and in what order to do this or that. What should one begin with? Openings or endgames? Should he play open or closed openings, should he concentrate on main lines or 'subsidiary' variations? What is more important: a tactical mastery or a positional one?
Opinions of respected specialists, grandmasters and world champions differ greatly. Some claim that chess is 95% tactics, while others hold that the basis of chess is positional play. We should not take such statements seriously; they are worthless and only disorient people because each one reflects only a single facet of the problem. In fact, when we think over a dilemma, be it the one I have just mentioned or another one - for example, should we work to develop strong qualities of a player or to liquidate his weaknesses? - any unambiguous answer like 'we do either this or that' will be a wrong one. The truth lies in skillful combination of the opposite approaches, in search for an optimal proportion between them. And this proportion is individual for every particular case. ..." - IM Mark Dvoretsky (~2003)
"... The game might be divided into three parts, i.e.:- 1. The opening. 2. The middle-game. 3. The end-game. There is one thing you must strive for, to be equally efficient in the three parts. Whether you are a strong or a weak player, you should try to be of equal strength in the three parts. ..." - from Capablanca's book, My Chess Career
At https://store.doverpublications.com/0486206408.html , one can see page 42 of Lasker's Manual of Chess: "... nobody can wholly escape the dire necessity of compiling variations and of examining and memorising them. And therefore such a compilation, though a brief one, is correctly included in a Manual of Chess. Here follows a collection of variations essential in Opening play. ..."
@18
"if you don't manage to reach the endgame with an advantage there's nothing to convert"
++ Carlsen is famous for winning theoretically drawn endgames, i.e. waiting for a mistake.
https://www.chessgames.com/perl/chessgame?gid=2127373
So was Fischer:
https://www.chessgames.com/perl/chessgame?gid=1044663