FO put out a video about the offense too. One guy thinks the performance is fluky and not sustainable. His reasoning isn't very good though.
His reasoning isn't too terrible. It's what you'd expect from a statistician trying to look at this from a numbers perspective. He sees an event occur (team is much better offensively than projected), he looks at how that event typically plays out (team regresses back to projection), and therefore a safe/reasonable prediction is that it will repeat this time.
That said, I think there are reasons why we can at least hold out some hope/expectation that this might not be the case for us.
First, our OL seems to be improved. An improved OL is as solid as an upgrade you can make for expecting continued increased performance. It doesn't require a fancy scheme to work or skill players to produce at unsustainable levels above the norm. It just makes everything your offense needs to do a little bit easier.
Second, our offense was probably ranked far too low by their projections to begin with. Our offense finished strong last year. I think the overall assumption in their projections (as with many) was to look at how we were as a team over the course of the year, knock us down a peg for losing Russ, and then that was their projection for the year going forward but I think there were indications in how we played last year in the final games that this offense had potential to actually be quite good if our QB was on the same page as our coaches, which brings me to...
Finally, they simply overestimated what value Russ brought to the team and assumed that switching to Geno was an automatic downgrade. As they mention, a team that is vastly underperforming their Offensive DVOA projections is the Broncos. In fact, I believe our biggest issue as an offense was a QB who refused to work in concert with the rest of the team. By dumping Russ, we dropped our biggest liability (no matter how talented) on offense. I expected our offense to improve, but the FO folks--perhaps reasonably--did not.