1st, powerful/quality is not = guarantee. (...-.-' I say this every day)
2nd, try to analyze how play your MC's, if you see their names during the match, if they are active, if they shoot.
And in 2nd half if you don't see the name of one during 50', just change this for another.
To win 7-0 you need a good team in all lines, so yeah, is posible something fails.

Some seasons my better playerd was a MC, not a ST, and he did the 70% of the work, but, you now players are older, others come to the team, and now in my case the best is a ST. But, when one have a great MC, you can see the difference easy.
Try to see how work and participate your MC's in the game during some matches, and if you see that one, is worst in ststistics or do nothing just bring this player to the market and buy another.