As someone who is not an expert but has watched way too many Sunderland matches this year (~15-20), there are 2 basic problems:
1) That team is a disaster with no central midfield and with terrible service. I think they would regularly tie/lose to MLS teams.
2) Jozy doesn't have great off the ball movement and doesn't have the opportunity to do much with the ball when he gets it, because he has to drop deep then pass it off to a midfielder.
I also want to say there's been awful coaching, but that's kind of something that's too often thrown out by people who are ignorant the details of soccer coaching (like me).

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