re: "No fullbacks" according to O - Why?

Well yeah, football formations have evolved, even in the old days, a good offensive coordinator found ways to make his play calling less predictable. It's misleading to assume that they always used the I-formation. More common was the split back or pro set formation which allowed for more options:



Note that the FB and TB did essentially the same thing. Back then, fullbacks were more valued as runners. They weren't just additional offensive linemen.

And of course there were numerous other formations, including shotgun.