the one who claims "you must do X" or "you must do Y" are fairly easy to refuse. show them one counterexample! the rest is chess dogmatism or necessities of certain levels.
the more knowledge you have the better you will be, and i do agree with some of the people above, that having confidence in simplying a position into a win or draw is very useful but i can guarantee you, most games by class players are decided on mistakes (or mistakes not penalized) way before the endgame. "the endgame is important" school is usually old chess orthodoxy, which has its merits, but the burden of proof is on the one claiming absolute statement "this is essential" or even "This is important".
most noobs are noobs bc of lack of tactics, or positional understanding and to a lesser degree opening ignorance. no class player is at that level bc they didnt remember centurini's rule in bishop endgames, or memorized key squares in all pawn formations in K and P vs K endgame. hell even the number of games you will botch from not knowing how to build a bridge in practice at the class level wont be nearly as high as you think.
The one who claims that you must start from edngames is no other than the World champion Jose Raul Capablanca.
The same is repeated by another world champion Vasily Smyslov in his book about Rook endgames. It is repeated by the best trainer of all times Mark Dvoretsky in his series School of Chess Excellence. He specifically mentions that starting from analysing endgames can greatly improve a strudent's analytical skill. In the preface Kasparov mentions that he did exactly that in Botvinik's school and that was the "foundation of his chess playing life". Mikhail Shereshevsky , another great teacher addresses some serious opening problems by examining endgame positions and Yusupov in the preface claims that studying these positions will make a player play the opening better. Jacob Aagard claims that endgame training improves calculation and he highly recommends it to his students.
3 world champions and a trainer that has created junior world champions and grandmasters among others. In contrast with them we have what? You? Give me a break!
These guys understand something that on line patzers don't. What is it?
Endgames is not just fundamental endgames. It's endgame strategy which is very closely connected with everything you do in the middlegame and that is closely connected with everything you do in the opening. If you don't know endgame you don't know which pieces to exchange , you don't know which pawns to move and you lose several(actually almost all) chances to convert a small positional advantage into a winning endgame and even if you accidentally land on a winning endgame, it's very doubtful if you can win it(you most likely depend on your opponent's mistakes and pray to be several).
Without good endgame technique you are blind but you don't know it because you will never see the missed opportunities.
Now if we are talking for on line patzers then nothing of all this is important. Absolutely nothing. But for kids , it's a whole different story. There is no good chessclub teacher that doesn't emphasize in endgame. I had the luck to meet one and I had the luck to attend several lectures by others and they all agree that the best study method for talented kids is:
1)Endgames and
2)Annotated games starting from classics.
Why not tactics? Because once a kid improves his analytical skill studying tactics will be much easier and much more beneficial(not surprisingly Dvoretsky claims the same). Analytical skill is by far the most important skill for the novice chessplayer.
p.s. To those of you interested , on line tactics trainers are not recommended for kids. Books that explain the mechanism of tactics are considered much better. Mechanically solving tactics in an on line tactics trainer might have even negative results. In chess what matters is not finding the tactic , it's creating it. And if you don't understand it , you can't create it.
your source of authority here are two of the greatest endgame players and one of the products of the soviet school, which was very methodical and relied on viewing chess as a science. of course they will say that.
that is then this is now. the modern masters are not a product of the soviet school. long gone are the days everything yusupov and dovrestsky said was taken as gospel.
by all means study endgames, in fact, given how little class players can reliably learn of endgames, it is pound for pound some of the easiest useful things to learn but "importance" is different from convenient. the jump from class E to expert is 80% tactics.
Beginners should not waste their time with end games. The order of a chess game is opening, middle and end game. Learning should proceed in the same order. Learn a few openings. Try them in games. Then, practice middle game tactics & strategies. Then, focus on end game. Then, repeat.
Anyway, the first priority of beginners should be to avoid blunders i.e. not drop material.