Much of the debate in this thread is predicated on Archer playing RB. He is not a RB. He is a slot recevier, kick returner, and will play in the backfield infrequently, if at all.
That said - a 3rd round pick for this Steelers team, with its needs, is just too high for him. If the Steelers took him in the 6th, then ehhh, what the @#$%. I think the comparable to Archer is Tavon Austin. Both weigh 175 lbs. Both have elite speed. Both project as slot receivers/kick returners.
Austin ran a 4.34 40, Archer a 4.26.
Austin ran a 4.01 shuttle, Archer a 4.06.
Austin did 14 reps, Archer 20.
Austin posted a 32" vertical, Archer 38".
They are very similar. Last year, Austin 40 receptions, 4 TD receptions, a punt return for a TD, rushed for a TD, average 17 yards per carry on reverses, etc. and put up a combined 1,170 yards and 6 TD's.
That is not irrelevant. A slot guy who winds up being covered by a LB'er who runs a 4.7 40 is going to threaten deep, and likely force safety attention. That means one less DB to look after Brown, Heyward-Bey, and Bryant.
Just don't like a 3rd, where the draft is so deep and the team had so many needs.