I think that part of the label depends on what team you're on.
That's a pretty good analogy, except for the fact that Rivers is a bit tougher than McNabb. I mean, the guy plays with pain (Rivers), and McNabb was injured/hurt so often. But in terms of accomplishments, I think it's pretty close. McNabb was in the Championship game a bunch of times and the Superbowl once, but overall, yes, very close.
Rivers blows McNabb out of the water statistically, though. McNabb never once threw for 4,000 yards. Rivers hasn't thrown for less than that since 2007. I'd say overall Rivers is much better. I mean, Rivers' "down" year last year included 4600 yards and a 62.9% comp. The only thing that truly sucked about Rivers last year were his 20 INTs.
We'll never know, but I do agree that Rivers has been a pretty mediocre quarterback come postseason play with a 3-4 record along with some awful QB ratings/playoff performances. Overall postseason QB rating of only 79.2 with 8 TD's/9 INT's. Has always been a very good regular season quarterback, but has also fallen flat on his face (time and time again) during pressure situations/moments of postseason football.
I'm pretty sure that the Chargers regret letting Drew Brees walk in favor of Philip Rivers, and as a Jets fan, I'm just thankful that Miami was unsure if Brees' could remain healthy (shoulder) and ended negotiations for Brees in order to trade Daunte Culpepper.
With all that said, Rivers put up 3 consecutive regular seasons of strong (to great) performances before an overall decline in performance last season. Antonio Gates (his favorite target/weapon) being hurt didn't help the situation any. With Gates returning to (potentially) full health, I look for Rivers to put up another Pro-Bowl type of season. If I were a betting man, I just wouldn't bet against a quarterback such as Rivers; at least not until the playoffs that is.