My understanding is that the player rating is a composite based on the final score and the actual match stats. The game doesn't rate players on how well they've done their job.
IMO it doesn't really work very well at the moment.
In your example, the defender should really get a 4 or less if the opposition striker beat him 4 times to score.
I have won games 8-0 and my goalie gets a rating of 8 even though he's not had to make a single save...
Someone may make several key tackles and do well, but score an own goal. Invariably he'll get a rating of 5...
The opposition GK may have saved 15 shots on goal, but because I won 4-0, he'll get a rating of 5 or 6...
The solution would be to give each position a different composite score. This might take longer to compute, but could result in ratings that more closely match actual performance.
So a GK's rating would consist of:
<UL TYPE=SQUARE><LI>number of saves (perhaps including a difference for saves from close range v long shots)
<LI>number of mistakes (including spilling the ball, etc, which may not result in goal)
<LI>distribution from restarts
<LI>other factors, like fouls, yellow card, etc
</UL>
Whereas a DMC might have ratings based on:
<UL TYPE=SQUARE><LI>goals
<LI>assists
<LI>tackles made (bonus for key tackles)
<LI>number of opposition attacks broken up
<LI>number of intercepts
<LI>fouls made (penalty for silly tackles leading to opposition chances)
<LI>pass completion
<LI>yellow/red card
<LI>work rate, for example by measuring number of ball contacts
<LI>anything else I can't think of right now
</UL>
The point being, that each position would have ratings based on a set of positional parameters that rate each player independently from the final score.
I'd love to read messages like:
<UL TYPE=SQUARE>
<LI>"{player} was the only one to try and stem the tide against {team}"
<LI>"{player} was instrumental in the win, despite poor performances all around him"
</UL>