Is it because of your GK and his rating or is it because of the whole quality of your team compared to your opponents? He has mostly 8s and only a 9. The only positive in there is the MoMs.
GK ratings are likely to be biased in this game. For instance, a GK make no saves but get an 8 (which is showed as 7.5 or in the detailed match report). 8 does not mean much. Some 3-4 star GKs might be doing better than him with 9-10 ratings and a lot of MoM. This is the concern. By the way, your GK can be considered to be 8 stars and not 7 stars. Take into consideration that a player who is 3/4 the way to the next star can be considered as being a star above in overall quality, and if he was power-trained, it is most likely that he is already an 8 star or above GK if you consider the goalkeeping attributes only.