I think paladins' being unable to parry, cleave, jab etc because of the need to balance a called mount is a pretty weak argument - and I'm seeing hopeful signs that WotC agrees.
But the Paladins are not unable to parry, cleave or jab. They do these all the time, it's part of the
astract nature of combat, you don't need to say "I parry" every round, it's already subsumed in the fact that you are moving your arms while fighting (your Dex to AC, even when the modifier is negative it's still better than standing still = treated as Dex 0).
Just because the Fighter has a
special ability called "Parry" doesn't mean everybody else is not parrying! It means that the Fighter can choose to parry
better when he wants to.
As a matter of fact, there are many other ways in the game to "parry better when you want to". One of them for example is taking the total-defense (or whatever it is called) action. Sure, you have to give up your attack this turn, so what? The game is full of trade-offs and this is perfectly in line with the idea that if you want to "parry better" then you have to so something else a bit worse. And the Fighter is doing a trade-off too, if he chooses Parry he's not choosing Deadly Strike or something else.
So you have Total Defense, surely there will be a parrying option or two in the narrative module, and there will be at least one feat granting some defense bonus which even if the fluff doesn't mention parrying specifically you can probably just refluff that. But no, you want to step on the Fighter's toes at any cost and steal his stick? Why can't I say then that my Fighter must be able to steal your Paladin's sticks, all of them? Why can't my Fighter learn Paladin spells or abilities or auras, he could after all be receiving a bless from above for praying hard enough. But guess what... they can! It's called "multiclassing".
No, the fundamental problem here is not balance at all, it's about making classes
different, if they can provide a good explanation why then great, otherwise they should just force it
artificially. Call it gamist if you want, but it's a known fact that the Fighter class suffered for many years from the problem that people just didn't play it single-class for long and after a few levels they just used a few levels of Fighter for some bonuses.
Therefore either you go with Tony Vargas' suggestion to ditch the Fighter class completely (but then you have to explain to countless players why they have to shoehorn themselves into Paladin, Ranger, Barbarian when they don't want any of those specialist concepts), or you accept the fact that some class abilities just need to be "protected" or "restricted".