Did you see the Catches Nelson and Roosevelt made yesterday? Yes, Fitz made good throws, but they were also extremely difficult plays for the receivers to make.
As far as defensive players, as a whole the D hasn't been great, so it's not surprising that there aren't more gems there. But...
Kyle Williams was 5th round pick I believe. And how is 6th round (Arthur Moats) not late round? George Wilson who has played well was an UDFA.
And as for the offense:
Fred Jackson - undrafted
Demetrius Bell - playing better than most people expected, and looks to be at the very least an average starter at LT
Cordaro Howard - has received a lot of playing time as an undrafted rookie and has looked like starter material (provided he gets some experience under his belt)
David Nelson - has made great td catches the past two weeks, also has moved the chains and is a reliable big target
Steve Johnson - a 7th round pick now has 10 TDs (ties the franchise record for a QB / WR combo in a season with two games left)
The point is that we seem to have a lot of players who were drafted very low or not at all who are over-achieving. In addition to these low round picks, we also have a lot of unheralded players who were originally drafted by other teams who seem to be coming here and playing well (e.g. Urbik, David Martin, not to mention Fitzpatrick.)