Although your player salaries are on the low end for the league, it's not too bad. I'm looking at your roster and I think the big thing to learn is how to manage game shape. Most of your top players are in poor game shape which means they will underperform during games.
Players in strong or proficient game shape will over-perform. Generally you want to shoot for 48-70 minutes played every week, per player, which will help improve game shape over time. So most teams play their starters 2 games per week, and play backups during scrimmages.