If Feats aren't allowed, the entire discussion is irrelevant, so it makes zero sense to even bring that up. You have to use the default option, like it or not, in that case.
As for "a versatile concept", I'm not convinced that, outside of point-buy, which is, ironically, where CharOp is most focused, the default is any better than the Feat + Skill option. You can always use the Feat to buy something that makes you more versatile, likely vastly more so than.
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Joe Liker
Wow, that's quite a pile of strange assertions you've got there.
If your DM creates a situation where a low/moderate-CHA PC is FORCED BY THE DM to make a bunch of CHA-based skill rolls, which is your example, then +1 CHA is not likely to help much. Role-playing-based bonuses, or role-playing in such a way as to obviate the need for skill checks will have infinitely more importance and value. Yes, I would definitely say that if the reason the mission you described succeeds or fails is Diplomacy checks (or the like), that's a really bad setup and the DM is probably bad (unless he's expecting it to fail and has some sort of fail-forward setup).
What you don't seem to get is that almost all your points rely on the DM forcing the PCs into a situation where their failure is near-certain. For example, you say it's best if all the PCs pass the jump check, but you act like +1 DEX will help there in a meaningful way. It won't. AT MOST it changes a modifier by +1, i.e. 5%. For one PC. So it improves the odds of the PCs succeeding by something like 1%. That's if it does anything at all.
You keep talking about "reasonably good" and so on, but that's nonsense. The difference between +0 and +1 is not "reasonably good". It's 5%. You seem to be labouring under some bizarre illusion that +1 to a stat determines whether you are a liability or an asset. It does not. It's bizarre to see people claim that it does.
The valid point you've made, that I can see, is that the Encounter/LFR people, the prime CharOpers of the world, will be using this, and will CharOp with it by intentionally buying odd scores. That's true. Ironically, though, it goes against what Mistwell was saying, because he appeared to be suggesting that the six +1s option was LESS CharOp-ish! Ironically it's more CharOp-ish.
Let's be clear, too, I never called it a trap. I specifically said it wasn't. But it's less valuable than it superficially appears.