I have the same problem. I always end up winning games by blowouts (4-1, 5-0) OR I have to win by these margins: 5-4, 4-3, 5-3, etc. It's quite annoying.
When I watch how they score on my defense, their goals always come from a through-ball splitting my 2 CBs or from a cross out wide. It makes my CBs look like idiots. Another problem I've encoutnered is that my team can only score from quick counters. Yet, I have unchecked the "Counter" option in tactics and anything like that.