Sure, I doubt anyone would argue that fact.
But the question is: is the game "no fun" (or even significantly less fun) if you can't qualify for certain feat trees?
In my case, the answer is no, it doesn't significantly affect how much fun I have playing the game. For others, it apparently does.
Say you're playing a Rogue and decide to go with TWF in combat. With your bunch of sneak attack dice, that's a good option. I'll even go out on a limb here and say it's the only really mechanically sound combat option for rogues: ranged sneak attacking is a pain (as it works only at very short range and archery takes a huge bunch of feats [note that Manyshot is barred to this character as well, btw]), and sneak attacking with a two-handed weapon just doesn't work as well.
However, if your Dex is merely 14, you're never going to get Improved Two-Weapon Fighting, even though that is your schtick. You're never going to improve at what is your only sound combat option beyond what you can already do at first level.
You're not only being less powerful than a Rogue with Dex 18, which as you pointed out doesn't mean anything, since character power isn't absolute and isn't what makes a character fun. But in this case, you're also gimped in (mechanical) character growth. Sure, you can spend your feats on Skill Focus and Chaos Devotion or whatever, but in combat, which is a lot of the time, you're prevented from using those feats that would complement your play style.
Now I don't say such a character can't be fun. But on the mechanical side, this just seems like a case of bullet-to-foot. Which is why I'd think twice about playing this character: I can't even get significantly better at what I'm supposed to be good at. I don't have the
option of taking this Rogue into combat and be more than a little useful.
This doesn't
have to detract from the fun of playing the character. But it narrows what you can do with him/her, mechanically, which might just cramp your style on the roleplaying side, as well. No "quickest two blades you never saw" concept for you. Merely "two blades of average quickness" possible here. Good for you if that's enough for your character concept - but more options are a good thing, as I'm so fond of saying.