The analysis assumes that PFF grades ae objective and unfallible and that may be very untrue. What if arm length does matter but PFF ratings are too subjective to be able to show the difference. Plus there are other factors like experience which can mitigate physical deficits. If you were actually trying to assess arm length in a controlled setting you would control for things like experience, strength of the overall line, number of times you are in pass protection versus run blocking etc. So really it tends to show that some players tend to overcome their physical limitations by using other skills. But all things considered it makes sense that longer arms would be an asset just not the most important one.
I doubt any of the grades or analysis is very scientific...which is why it's best to go with 'can the guy play or not'.
Some of those current guys with short arms who are dominating may very well just be better players...like you said it'd be pretty tough to determine just what sort of an edge or advantage having long arms actually gives a player.(if any)
Even saying longer arms is an asset is just a theory one that makes sense like you say...one thing I've always thought about is that having longer arms could also slow them down on the way up and into the opponent. So the shorter arms have less to travel to reach full extension(depending on what you're doing)...I'd imagine if you are doing a drive block and you can whip your arms into position and get them up and in position quicker the length of your arm isn't the end all be all for that and could actually hinder you if it affects your hand speed.
COMPARES TO: Emmanuel Sanders, Pittsburgh Steelers - Some will compare Richardson to Sanders' more established teammate Antonio Brown. Until Richardson (and Sanders) catch the ball with more consistency, however, each is likelier to earn more of a complementary role in the NFL despite natural playmaking ability.
Highlight reels are dangerously misleading. RIchardson will not go before the third round IMO
He shouldn't go before the 3rd...no one should really be stating otherwise...he is just another WR with potential in this draft that seems to be a bottomless pit of WR talent.