I agree he should be most advanced out of the MFs in a 3 man MF with Davies and Delph holding at the moment with the players we have, you couldn’t ask Gylfi to play in a more defensive role.
But when we play 4 in the middle we become very defensive and the the 2 central MFs don’t get to link up with the 2 up front that’s left more to the 2 wide-men.
Which isn’t playing to his best strengths, with 2 in the middle he could get forward more if one of the 2 wide men holds there position and tucks into cover the space, you don’t see that so I would say both central MFs are more concerned with holding a more defensive position.