There's a difference between saying Rivers doesn't have an "NFL arm" and simply acknowledging the truth, that he does not have a top half arm for NFL starters. In fact, among NFL starters I would say his arm ranks in the bottom tier...with guys like Brad Johnson, Brian Griese, Chad Pennington, Charlie Frye, Rex Grossman, and Marc Bulger. Drew Brees, Trent Green, Alex Smith, and MAYBE Tom Brady could be placed in another group just above those guys...although I personally set Rivers' arm strength below that of Brees, Green, Smith, and Brady.
I mean, that is seriously just being realistic. Those that disagree with me REALLY need to look at the NFL team-by-team and realize that the guys with the best arms tend to shake out as the starters. Not in my wildest dreams would I dare to say Rivers has a better arm than Frerotte, Losman (or Holcomb), Palmer, Roethlisberger, Boller, Dilfer, Peyton Manning, Leftwich, McNair, Carr, Plummer, Collins, Eli Manning, Mark Brunell, Drew Bledsoe, Donovan McNabb, Joey Harrington, Brett Favre, Jake Delhomme, Chris Simms, Mike Vick, Aaron Brooks, Matt Hasselbeck, Daunte Culpepper, or Kurt Warner.
So, when we say bottom-tier...keep in mind that of the 36 guys that I named, 26 of them belong in a group of guys who have top quality arm strength. Within that group of 26, I'd say there are probably about 10 guys whose armstrength distinguishes them from the group and they would therefore have "top 10" arms (Culpepper, Palmer, Leftwich, Boller, Collins, Bledsoe, Favre, Vick, Brooks, and Delhomme). Of that group of 10 guys I would isolate the top 5 as being Palmer, Leftwich, Culpepper, Bledsoe, and probably Brooks (truth be told). Favre would have been on that short list were he younger than he is.
So yeah, you can keep tiering it up if you want. But the point still stands. Rivers has bottom-third armstrength among NFL starters. When I argue that his armstrength isn't up to snuff for this offense, it is merely an acknowledgement that Scott Linehan would very rarely consent to a starting quarterback that did not belong in that group of 26 guys.