If both sides use the correct tactics, an average 10q higher team would more likely win. I'd say something like 95% or 18 in 20 games.
The quality advantage is much less than you would like. When you have many players getting form 6 or lower, you are not managing your team well enough to ensure domination.
Morale is not much of a factor for player performance. In fact, the natual change in morale after match is an indication of player fitness.
Don't judge players solely on the stars, but by their overall pitch performance.
If you think a higher quality team should always win you've vastly underestimated the complexity of the game and I don't think you are so "dedicated" as you claimed. You may have tried your best but it didn't work as you thought, the situation won't improve unless you find your decision errors and correct them.
Tip: Bench or fire the worst performing player in the last 5 games, and find someone else to replace him, no matter the quality, one at the time. Repeat the process you will eventually have a top eleven of motivated and powerful players that is very difficult to beat. RL regular lineup is pretty much the same thing, really.