It is true. The window for the Broncos is ending soon if it did not already. Osweiler maybe the solution but that is an unknown at this point. NFL teams live or die based on their quarterbacks now more than ever. Manning is older accept it.
Eh...whatever. Peyton is not the main problem with this team. Even at diminished capacity he's still better than any other option out there. In the end it's the Broncos' overly-conservative and frankly not-good-enough coach who will be the team's undoing. If the Broncos fail this year Peyton's likely gone and Fox most definitely is, so it'll be a moot point with the franchise hitting the reset button.
Someone on Twitter rightfully pointed out though that if the team runs too much people question Peyton's ability, and if they throw too much they're accused of relying on Peyton too much. It's a no-win scenario.