At least your stadium is much bigger than an average lvl3 manager gets.....but the game never garanteed that a better team always win against a weaker opponent.
For example, when I was a starter, average team at level2, i won a friendly match again a level 5 player who has all players 20 levels above me.....2-0 for me, and i wasn't even online.
So, you have a bigger chance to win, but never een garanteed win.
But I can understand your frustration!!!