My point is that in top eleven 3 at back are more powerfull than in reality. I don't know, maybe in TOp11 fullbacks are not so essential.Also, a packed midfield give way too much power. Much more than real football.
If your opponent use wingers (AML/AMR) you drop back your ML/MR to DML/DMR and weirdly, you're still fine. Therefore, even if the opponent tries to counter you, you can response quite well. You can just drop 1-2 midfielders or put them higher up and you can pretty much response to he's counter. The real counter would be long balls counter attack and staff like that but again you can still drop 1 MC to DMC and be more solid at back.
That's my feeling. I personally use a variation of 3-5-2 with much better results than I hoped for and each opponenet I've ever met with a variation of 3-4-3 or 3-5-2 did actually pretty well.