In this case our math isn't all that different. I was suggesting that instead of the DnD point buy, stat points instead offer diminishing returns not based on level but by current stat, in math that closely reflected the point buy seen in DnD character creation.
The thing about that is that in point buy, purchasing higher stat costs more to compensate for the fact that the player gets full control over a process that traditionally involved rolling a set of dice(3d6, hence the 3 point minimum, and you can remove points below the default 8 if you wish so).
It is in no way related to actual balance, as far as balancing encounters goes.
The system I'd have in mind would already be more generous than classic D&D, and not having those penalties is a deliberate part of that.
As far as adjusting the value a point has, if it was to change/diminish as you increase the number of points in a single stat, a more elegant solution than thresholds(which encourage min-maxing) would be to have a formula that adjusts the value.
