Hi again,
Thank you very much for the feedback, I really appreciate it.
When playing formations like 451V, you need very strong AML/AMR and DMC, in my opinion. However, this doesn't mean that only those are important, or that you should focus exclusively there. I suggest to treat all players equally, and to create a balance in your team. A balance is crucial, along with 3-4 solid substitutions (for rotation purposes).
I used to focus on particular positions as well, while completely neglecting others, until I realised that in case my 'strong' players had their bad days, I was in complete trouble.
I hope this helps.
Cheers