The argument isnt what he called himself on twitter (which is the dumbest argument I ever heard. shyt I call myself a TE on my twitter page too, so I should get paid like one) and its not about what he actually is on the football field. Its about the letter of the collective bargaining agreement.
A formula encompassing the salaries of players at the position in which a player “participated in the most plays during the prior League Year,” is used to determine the value assigned to a Franchised Player.
If you feel that he lined up 2/3rds of his plays in the typical wide receiver position, then he should have been paid like a wide receiver. Simple as that. Thats exactly what the agreement states. If, on the other hand, you feel as if a TE can line up tight or wide and still be designated as a TE, then he should be paid as a TE.
Based on my interpretation of the agreement, I would have to conclude w/ the arbitrator. I still hope a team out there pays the man what he's worth, tho.