Form over Quality!
Just because a player has 6 stars of quality, doesn't guarantee them to be a good player. At one time, I once purchased 3 consecutive MC's from my scout list and all of them seldom got above a "5" rating. A 6* player with a "5" rating will be outperformed by a 3* player with a "7" rating. If you have players like this in the middle of your diamond like I did, your team is going to struggle with lesser quality teams.
If you're not maxing win bonus, morale and condition, maybe doing so could help improve their performance. My 3 MC's sadly wouldn't get above a "6" with the all three maxed. Some players don't play certain formations well and others don't play well no matter what the manager does (regardless of quality).
A change of orders is another option. I myself am not well versed in the 4-1-2-1-2 ND, but their are several very experienced players on this forum that will have very good advice in how to setup this formation.