The biggest change in the Broncos is the coaching staff.  The offense under McCoy allows Siemian to audible to multiple plays, quarterbacks choice.

When Kubiak ran the show, Siemian was allowed to audible to only one play preselected by Kubiak for that situation.  If Siemian didnt like the original play, he had one option to change to.

Nothing against Kubes, hes served the Broncos well both on and off the field, but the ability to allow Siemian to use his intellect and select whatever play he desires is a drastic improvement, as long as Siemian is intelligent.

So far, Siemian has been just that.  Wise beyond his years.

Its a massive upgrade brought to us by a collection of factors, (more open coaching, more aggressive and creative playbook, the utilization of Siemians inherent intellect, and a good draft of offensive support players by Elway, etc)
which has the Broncos first in passing touchdowns and first in rushing yards.

This bodes well for the next ten years.  Very well.