Incomplete evidence at best. Was there a sudden spike in offensive stats in 1978? Sorry, but those aren't major rule changes, and the whole Indy-New England thing was a tempest in a teapot.
Incomplete evidence? Look at the stats, and see just how much of a statistical jump there was in the passing offence, from 1977 to 1979, for QBs AND WRs alike.
I mean, in just two seasons from 1977 to 1979, Top passing-totals jumped, from hovering in the low 3000s, high 2000s to the 4000s.
There was one major rule change which accounted for this, and it was the Mel Blount rule. Now, receivers weren't being killed running their routes.