For all intents and purposes, I had this match won, but because it went to stalemate, I ended up losing 5 points despite clearly having every advantage.
You just have to remember to avoid stalemate when you're way ahead in material. That will come with time and practice. (Instead of Qb1, Qc4 would have been mate.)
And when the game is a draw, if you're the higher-rated player, you'll lose a few rating points.
If you draw against Carlsen, then you win rating and he loses rating.
Stop complaining about losing points; learn to win “won” games. You were given gifts which you squandered; your result was deserved. At move 22, you have a significant advantage; play BxN not d5, then Qf6 bringing Q in play on f-file or a1-h8 diagonal. Finish it a few moves later.
Your opponent walked away with 1/2 pt from a lost position, smiling all the way. This should make you mad enough not to let it happen again.
It hurt your ELO because he is much lower than you, and so chess.com punishes you because you SHOULD have beat him, by the numbers.
For all intents and purposes, I had this match won, but because it went to stalemate, I ended up losing 5 points despite clearly having every advantage.
A player with a higher rating is expected to have a greater probability of winning a game, so a draw would not be good for him.
Almost all sites with chess ratings will deduct rating points from the higher-rated player to denote the failure of the higher-rated player to win the game. Stalemate is no different from other draws, and it can be painful when the stalemate pop-up appears right in front of your computer screen.
Any derived advantage preceding the stalemate would be disregarded as stalemate is a situation of parity in chess (to allow the weaker player to have that glimmer of hope).
For all intents and purposes, I had this match won, but because it went to stalemate, I ended up losing 5 points despite clearly having every advantage.
For all intents and purposes except for actually winning the game. In order to win in chess, you must put your opponent in checkmate, or they must resign. Having a material advantage isn't the same as "basically winning the game" in chess. Luckily stalemate is pretty easy to avoid as long as you watch out for it. When you have a large material advantage, especially against a lone king, just remember in the future to check that the opponent's has legal moves available.
As to why drawing causes a change in rating - If you draw against a higher rated player, you will gain points. Similarly, a draw against a lower-rated player will cause you to lose points. It is significantly smaller amount than a win or a loss would give, and against a similarly rated player it is often just 1 or 0 points.
When you are much higher rated than an opponent, however, you are expected to win the match, not just draw or lose.
For all intents and purposes, I had this match won, but because it went to stalemate, I ended up losing 5 points despite clearly having every advantage.