There is more to it than any of that - for example, it's possible to get more possession by having more midfielders, better passing stats (or overall quality) in your team, playing short passing instead of long etc. Of course a big one is to be present for games, and to have a full crowd for home matches
If you do all those things, you may get more possession - but it's not guaranteed
And of course even if you do have more possession, that doesn't mean you will win those games necessarily
Finally, yes, AMC/R/L and DMC/R/L are midfield positions