Elo is measurement of probability of success, success is evaluated by your ability to play the game, your ability to be successful in the game is based on 1 of 5 major skill areas that can be further sub-divided or labeled. Ergo your ability play well has a relationship with Elo.
How is this point being missed...
You people are chosing to ignore the preface aren't you...------^
Whate Elo measures and what it takes to be a good player are 2 different things, one having an indirect impact on the other, but still different, and you are mixing them up.
Elo = % of win
win = be a better team
be a better team = have better players overall
have better players = each player being better
being a better player = points 1 to 5
So what you are are saying is completely valid and very useful on how to improve as a player, and of course being better improves your chances of winning, but it's not 1:1, it's more like 1:5, because you are 1/5 of your team.
That was my point, that there is a relationship indeed, but it's not direct, and Elo isn't purely a measure of a players skill, it involves a lot of other things.
Player A is good enough to be at 1900 Elo, but he only plays 4-5 games a week because he has other things to do.
Player B is not as good, say ~1500 good, but he plays 40-50 games a week.
If both start at 1200, chances are, that by the end of the season players A and B will be around the same Elo, because the game will not have enough data to rate player A accurately.
Players C and D have a very similar skill level and they both play the same amount of games, but player C was lucky and won more of the first games, he ended 7-3. Player D on the other hand was unlucky and ended 2-8.
These games are worth ~40 Elo each, so player C now has 1360 Elo, and player D has 960. Those first 10 games created a 400 Elo breach between them, and now it will take a ridiculous amount of games for them to get to the same Elo.
PD: I'm not saying that Elo is not each players responsibility, it is, and of course if you can contribute more to your team you will have better chances of winning. I'm just saying that there is more to it than that.