The success rate of the defender and the "power" of pots is most likely two different issues.
Pots provide only the stated stat bonus. But with the way defense and combat is resolved, the defender probably has a bonus to "roll".
Imagine if it was pure stats and no "random" change to win, the game would be very much in the hands of a select few of untouchables. At least now, even the most weak has a "chance" to defend against the strong.
That's to protect the overall player base and also to ensure a level of balance.
Just as people have a chance to fail on the super weak, they also have a chance to win against the super strong.
As you can see by the factors the dev's have referenced, x5, that incredible str differences in the game.
To make change would further unbalance the game.