It is true that point buy won't allow you to play superman, or Forest Gump for that matter. But to say you "have access" to the ranges 3-18 is also disingenuous. You don't have access to any numbers at all. You are handed the numbers that luck gives you.
If that's what floats your boat, great. We shouldn't have to get a lawyer to construct the proper legalize to say that "with point buy I can build a character within known constraints of the game system to the vision that most closely fits my desired ...."
Well, you get the idea. I should correct that. You won't get the idea. You will never accept that for me, point buy lets me build a character whose attributes roughly match what I want. Because I accept that all games have constraints.
You prefer rolling. I prefer point buy. That's all.
We each have our preferences, true. But when we list the advantages and disadvantages of each method, we may state something as a fact about that method which is not actually true at all.
You stated that 'point-buy lets me create the concepts that I want'. This may very well be true, in that only you know what you want. But you stated this as if one of the advantages of point-buy is that it lets
players who use that method create whatever concepts they want, and that is demonstrably
not true.
And, no, it's not just about 'power-gaming' either!
I could walk into a bus station and be part of a crowd of 100 people. If those people were all statted up in D&D terms for Str/Con/Dex/Int/Wis/Cha, there would be an infinitesimally small chance of every single one adding up to the same point-buy! Yet every single one would have six stats of 3-18, because this is the basis of that bell curve: it models the population.
Every single one of those people, being an already existing 'character concept', is by definition a
valid concept. But a tiny fraction is available through point-buy. They are
all available through rolling!
So, if what I 'want' is to play one of those concepts, then the vast majority will never be available through point-buy.
Six stats, all ranging from 3 to 18. That's a lot of possibilities. Six stats ranging from 8 to 15 is a tiny fraction of that. Six stats from 8 to 15 which add up to exactly 27 points is a tiny fraction of that tiny fraction!
So the idea that, when comparing rolling to point-buy, it's the
point-buy method that lets you play the concept you want? No! Point-buy is much, much more likely to
prevent me from realising a concept!
"Oh, but it lets players play any concept they want
as long as that concept adds up to 27 points" is the 'One True Scotsman' argument. It may be the more precise way of stating why you prefer point-buy, and it would at least be an actual advantage of point-buy: enforced balance. But that is not the same thing as 'point-buy lets players play the concept they want'.