Except that SE is not obligated to make every Job balanced with every Class if they don't dictate restrictions. SE does not have to maintain the illusion of balance between Archer-Paladin, Pugilist-Paladin, Lancer-Paladin, Marauder-Paladin, and Gladiator-Paladin. Archer-Paladin can totally suck compared to Gladiator-Paladin and SE wouldn't have to do anything about it.
That's because the player community would pretty much give a collective "Duh, of course! What else did you expect??". That would also hold true of Marauder-Paladin vs. Gladiator-Paladin. One may edge out the other in some aspect or another, but SE does not have to keep them balanced, because they let you have the entire gamut of possibilities for Paladin ... both great and not-so great.
Once SE states there can only be Marauder-Paladins & Gladiator-Paladins, they MUST keep the two balanced because their statement/restriction implies one should be as effective as the other. If one becomes more effective as a Paladin than the other, it invalidates the entire premise of having the restriction in the first place (i.e. to prevent not-so-great Class-Job combinations). So SE would have to constantly keep the two balanced.
Now multiply that constant balancing act across all the SE restricted Class-Jobs combinations ... versus ... having no restrictions and only nerfing two or three overpowered Class-Job combinations.
One may disagree with the policy of nerfing, but it is far easier and more efficient than re-balancing entire subsets of classes and jobs whenever a new Job or Class or Ability is introduced.