I don't have the stats in front of me but also, he wasn't doing it in-line! He was offset, someone correct me if I'm wrong but I don't think he took many or any snaps attached to the OT. Blocking from there, the angles and the quality of player you're blocking (DE's, LBs) is far more difficult than blocking offset or detached from the line and that's not including pass-set blocking or chipping along with run blocking.
I've argued this with WR but best to think of F and Y as two separate positions that hold the title "tight end." Yes, there can be some interchangeability but that's more the exception and not the rule.
And from what I remember, Fergy's blocking was atrocious for the first 1-3 games he was out there but surprisingly he started putting some very good reps shortly thereafter.