And i understand what it is D&D system. I'am just saying why there is no damn difference.
If you were actualy understanding D&D system ... you would know there is difference.
There is no "randomness" in jumping ...
Personaly i would like to see some easy (dif. 5-7) rolls for sometimes falling prone, especialy when we jump at the edge of our jump raidus ... but there is none, therefore you allways sucess ... and therefore you imediatly see difference.
But persuation rolls are random ...
Your 12cha would fail, if you roll anything between 1-16 ... You rolled 17-20, therefore you were lucky.
Your 16cha would fail, if you roll anything between 1-13 ... You rolled 1-13, therefore you were just unlucky, thats all.
But you would sucess in second example if you roll 14-20 ... as you can see, if you do the math, your chances are almost doubled (4/20 vs. 6/20) and that is the difference.

Yet that is all it is, a chance.

The difference that you claim is not there is in long run ...
Your 12cha hero will probably be failing more often, than your 16cha hero ...
The world is not suppose to work like "i have 20 charisma, now i persuate anyone anywhere, and anytime into anything" ... and thank gods it does not. :-/