You know what, you do have some valid points.
Here's what it is for me: we just don't really have enough data to know where most teams really stand. Part of that will always be the case in CFB as there are 120+ teams and only a VERY limited number of games played by each team. The fact that there isn't all that much cross-over between leagues further compounds this problem (even the teams that do a nice job of trying to have a good out of conference schedule will only play 2 or 3 half decent teams from a P5 conference, at the most). So our sample size will always suck.
But on top of that, preseason rankings bias everything way more than it should. An easy example from this season is Wisconsin vs LSU. Both top 15 teams when they met. Close game that sees Wisconsin supposedly piss down their leg and lose (or the Hat pull another win out of his magic grass filled hat, if that's your fancy). So LSU moves up because they beat the #14 (preseason) team. But it turns out Wisconsin is 1-dimensional and probably not that good this year (their running game is nice, but aside from that their D is OK, while their passing game will make you claw your eyes out rather than watch it). So is that really a good win for LSU? Should they really have been a top 10 team when Miss St. played them?
The answer is I don't really know. But in all reality, it's probably a no to both questions.
What I do know is that we shouldn't rank teams until about the 4th or 5th week to eliminate any bias of what people project about a particular team.
I certainly think that's where some of the backlash against the SEC is coming from; having so many teams that likely didn't deserve their preseason ranking (e.g. USC, LSU, Mizzou). The catch is, no one deserves their preseason ranking because preseason ranking is a stupid endeavor that only biases people to those irrelevant thoughts about how good a team should be, which often reverberates through the season.
But those early rankings can color the rest of the season. TAMU has 1 "good" win over USC (the same team that beat Georgia and ECU, but also lost to Mizzou and UK; talk about a schizophrenic team), and another over Arkansas (who knows what to think of them). Then 3 "good" loses (whatever that means, particularly when they weren't all that competitive in any of them, especially against the Tide). So how good is TAMU then? Ignore rankings and really try to parse that out--when you do that, it all becomes a big mess. A wonderful, beautiful mess that is the college football regular season.
TL;DR: Preseason ranking is bullshit and needs to go away.