Siemian should obviously be the starter, & it's not close. 
But that deep incompletion to DT... ugh. If Robinson doesn't grab him, it's a perfect throw, & a 43 yard touchdown.
One play DEFINITELY wouldn't(& shouldn't) change the fact that Siemian is WAY more prepared to start. But it would've been cool, let Paxton take a breath, & MAYBE even given his confidence a boost.

It seems like most of the world outside of Denver forgets that last year was ONLY Trevor's 2nd season, his 1st as a starter, our O-line & run game were horrific, & he only played 3 & 1/2 games even REMOTELY healthy. 
Even MORE baffling though, are the critiques about his arm strength & athleticism. He's not packing ELWAY'S cannon, but he can make EVERY throw that an NFL QB needs to make.
And in those 1st 3 games where he WAS healthy, there were a NUMBER of times on 3rd & mid-yardage downs that no one would get open down field, & he'd take off around the end & get JUST enough for the 1st down, & keep the drive alive.