That's the Catch 22, yeah. So far it's worked against mediocre teams, buying us some time without costing us a game, but we can't count on the D taking away 3-4 balls every game (that almost burned us last night, when they caused and instantly snatched a pair of fumbles just a beat after the whistle) because that's another way they fade when tired (and I'm convinced 4th qtr fatigue caused KCs final TD.) Simms and Nantz like noting our D's a classic example of trading size for speed, and thus more prone to fatigue (fortunately they have Mile High to aid conditioning.) It's annoying because it's true.
The line must figure out/remember how to do its job, sooner rather than later, else the wheels will eventually come off the bus. Manning can't cover for awful protection every down, and the D can't cover for awful run blocking every game. One of the tweets posted early in the Gameday thread pointed out we keep getting in trouble because we keep lagging behind dial-a-down, finding ourselves in not only lots of 3rd but 2nd and longs, and that's because our running's so nonexistent early down runs are equivalent to incompletes, leaving us with all-or-nothing 10 yd passes every series.
Mind, I still feel short passes should only be used situationally (e.g. so defenses don't drop 7 deep or send the house the instant they see shotgun, or when they're expecting a run on 3rd and 3, not that any D's expected that then since the early '90s.) But when EVERY play's a 10+ yd pass attempt because the offense can't get a 4 yd run even if the D INVITES it, that's too predictably easy to stop.
Manning can still get it done, but could NEVER get it done ALONE. He and everyone needs protection to burn Ds for stacking the box (especially when they blitz,) because even with hot reads and track star WRs, they don't just teleport past jams and 20 yds downfield at the snap. And he needs a good enough run game blitzers and coverage LBs/safeties must watch the RB out of the corners of their eye, control their direction enough to change it quickly if needed, not just sprint for the QB or WR at the snap and ignore run fakes that couldn't hurt them even if genuine.
Oh, and I expect the glove back sooner than later, too; he'll need it this winter, and won't have time to readjust (but maybe he figures wearing it all season for two years means he no longer needs time.)