I take the OP's point that the powers the Oathbreaker gets are perhaps too classically evil to fit every ex-paladin that goes that route, and that the actual 5e subclass definition does talk about dark ambitions or serving evil powers though as I agree that isn't exactly how the Oathbreaker knight sells it it looks as though Larian have a slightly different take. I'd also agree that the proof of concept we see in patch 9 could do with a fair bit of work, but I find the overall idea works for me. I'm assuming we'll get Oath of Vengeance in the full release for our evil-from-the-start paladins, so the Oathbreaker will be reserved for those who initially swore one oath but grew to despise what it stood for with a zeal that mirrors the devotion they used to have for their oath.
For me, that's what distinguishes an Oathbreaker from just a paladin who has broken their oath. The latter is what we become after the oath is (in the game's view) broken but before we either recommit to our oath or to the Oathbreaker path. A paladin in this state can still do most of what they could do before, except channel their oath. I guess it would be possible to continue in this state indefinitely (I'm not sure if you can level up?) and though it would clearly not be an optimised choice, I can see someone making it for roleplay reasons. Particularly if we get multiclassing and can decide to progress in another class, in which case I think it would make a lot of sense to prevent taking new levels in paladin unless we'd committed to one path or another. To me it makes sense that a paladin who has simply broken their oath loses something and doesn't gain new divine powers, as it's not clear where these would come from. I guess you could argue they should even lose access to divine spells they had previously, though personally I'm happy to handwave that.
An Oathbreaker paladin as I see it is going a step further, and rejecting their previous oath with a fervour that actually forges a new, different (and darker, given the paladin options we have so far are the good ones) connection to the divine domains of the Realms. That's what gives them their new powers, not merely having broken their old oath. I find this idea interesting and one that opens up some interesting roleplay ideas, though the execution (including the availability of meaningful opportunities for oathbreaking) is a long way from perfect.
But paying 2000GP to restore your oath doesn't actually bother me as a stand-in for some sort of cost given that I understand there's only so much resource that can be justified for one class. Though I'd prefer it to be accompanied by some sort of overnight vigil animation as we rest the next night before our powers come back, or even something more sophisticated, but will happily use my imagination on this one if necessary. I do think the cost should increase each time we break our oath, though I guess that would have been unfair in EA given that the system for determining when oaths are broken is, let's say, in its infancy. As has been discussed at length on these forums previously!
Like Blackheifer, I hope we'll keep the paladin oath system and see an improved and expanded version in the full release.
