It also depends on your formation and arrows. I play a 4-5-1 V and with offensive arrows on my AML and AMR. They score a lot of goals. My striker however doesn't score much even though this season he is decent. Maybe its because he almost got 7 stars and is a lot better than the teams average...
My last season striker below the average team rating got like 4 league goals while the AML and AMR both got 17 or so. This year the AML has 11, AMR 9 and ST also 9.