Eh, I wouldn't call Nickelback posers. Now, do they have a pretty mainstream generic rock sound and lyrics? Absolutely, but I wouldn't call them posers exactly. Which I don't even know what "posing" as a rock band would be beyond claiming to be badass and hard (which I don't think Nickelback has done, I think they did at one point get labeled as "hard rock" or something but I don't think they've pretended to be especially hard rock, and I think they even poked fun at that in their one song, might've been called "Rockstar" even - honestly its a catchy song even if its terribly lowest common denominator generic rock song). They might not be that old school type of rock musician (I honestly have no idea, nor do I care to know if they live the lifestyle or are like super responsible straight edge; I always found it odd how there was this weird antagonism about someone living a healthy lifestyle in rock just so they wouldn't die young like so many others), but meh. Honestly now that I think about it that song I was talking about reminds me of that Weezer song that I believe came out years before. And it makes Nickelback seems like posers as Weezer/Cuomo are definitely not typical rock type and they probably rocked that style just as hard as Nickelback did.
Which, as far as songwriting goes, I thought the Beatles reputation for that was much more than lyrics and was more composition and them getting really experimental (when the easy route would've been to stay the course and keep the boy band thing going but instead they got pretty weird with things). I'll be totally honest, I'm not a huge Beatles fan. Same with Prince. They both made so much music, but most of it I'm just like, "not really my thing" but I can see they have talent and I do like some of their popular stuff. I remember a Cracked article that...I don't remember what it was about but one of the points was talking about the musical genius of some Phil Collins song (think it was "Shock the Monkey" and I was just like, WTF?).
For supposedly how untalented/untrained they were, I always felt like the Clash had surprising skill in that their songs seem to have a lot of variance (although I'm not sure they really did, I'm guessing they actually might've followed pretty similar aspects, if not outright been formulaic at times, but they didn't feel that way a lot), and just how the vocals and the instruments were in sync (by that I mean they felt tonally in sync as well, where the vocal cadence was really embedded into the riff/beats/etc). Its hard for me to consider them punk because their music just isn't what I think of from punk in a lot of ways, where it'd be rough (intentionally so) and just not have real melody or follow any manner of established musical style. Honestly for me, that's one of the bands that I'd point to if some one wanted to know what I'd consider to epitomize rock music. I guess in simplest terms, I wouldn't expect punk music to be catchy and rhythmic (yet I think most of my favorite punk music is; I'd definitely be a poser at punk shows and I'd "nope" and GTFO of GG Allin and probably even Sex Pisols).