I think like I said before in an earlier reply, playing a weaker team does give you an idea of your players. If your player CANNOT perform against a weak team with so many players out of position then he definitely is a useful player and deserves to be sold.

One thing I can tell you, try to play 4-2-2-2 Hexagon or 4-4-2 classic and play the players who you think will perform. Try it for 3 matches and see who is giving you consistent rating. Then retain those, replace the non performing ones with your sub/reserves and try another 3. Im pretty sure you will have a decent idea who is who and who is not supposed to be in your team

T11 is not rocket science. It throws you odd results here and there but it is not a complicated match engine.