Agree with everything you say except one thing - why do you blame Larian for this? It's WotC invention. You know, in line with "no players ever should feel punished for their choices, no matter what they do". JandK is right, once they WotC find out how to do the same thing with clerics, we will get a "broken cleric" or something (hell, we already have attempts of "atheist-cleric").
The blame for Larian is the implementation within the game. There was no reason to remove deity selection for Paladins, this was an arbitrary decision that actual goes against Forgotten Realms lore.
As for the Oathbreaker, there are other ways it could have been implemented. I said I think the idea of choice is good so having an "evil" Paladin for character creation is fine with me. However the falling of a Paladin as many have noted should be a punishment, not a side step. I get the limitations of a quest. Especially since that mechanic would be abused with people just repeatedly running the side quest. (More on that in a moment) There is also the fact that the game mechanics for determining if you have "fallen" is complex.
The solution within game mechanics and "reasonable" design choices is not overly complex. First a Fallen Paladin becomes a fighter at the same level. I would say either a Battlemaster or Champion. Both by description fit a traditional Paladin. Second if you fall and want redemption there is a steep penalty. Instead of 1000 GP make that number jump to 3000 and then if you do it again it doubles, and again it doubles. The doubling means that it will not be worth it to just pay the goal and act any way you like without consequence.
Clerics, as you are all noting end up posing a whole new set of issues. But we can save that for another thread
