Can't tell you how much I love "truth" delivered via interview, social media posts, and PR videos.
I also recall a fair number of people irritated with Crawford's take on his own rules. But I'm sure its much easier to accept a ruling from on high if you happen to agree with it.
But fine. We'll have to leave this a table issue then, since apparently PCs need to be protected from mechanical consequences for their actions.
I'm one of those who is constantly irritated with Crawford explaining the intent of rules when the text couldn't be bothered to do so, so I hear you there.
The thing with Paladins and Warlocks, however, comes down to this. Losing their powers isn't a balance point in 5e. There's no reason for it to be. Now to be sure, we more or less expect Paladins to be "good"-ish guys, but each Oath has it's own code of conduct, some of which stray from the traditional archetype.
And the thing is, there is a sidebar in the PHB that states exactly what should happen if the oath is broken. "At the DM's discretion, an impenitent paladin might be forced to abandone this class and adopt another, or perhaps to take the Oathbreaker paladin option that appears in the Dungeon Master's Guide". Not, lose access to powers. Not be turned into an ordinary Fighter. Just multiclass or become an Oathbreaker.
If the intent was to leave the door open for loss of powers or other penalties, wouldn't they have just said so?
Warlocks lack even this sidebar, instead the text reiterates two points. "Warlocks are driven by an insatiable need for power. No one makes a pact with a patron that doesn't intend to use the power thus gained" is one. And the other is "The warlock learns and grows in power, at the cost of occasional services performed on the patron's behalf."
Occasional. This is reinforced in the text with the section about "Creating a Warlock", where the player and the DM discuss whether your patron's demands drive you into adventures, or consist entirely of small favors you can do between adventures", as well as what the relationship between Warlock and patron is like.
Since loss of powers is never even touched upon, all you can infer from the text is that an angry patron might not grant you further powers- again, like the Paladin, you might be forced to multiclass, abandoning the path of the Warlock.
Now obviously, if the DM wants to impose additional restrictions upon these classes, they can. And the player has a right to accept that and play anyways, or not. But I can't see from the text that this was ever the intention of the authors, or that it's even hinted at as what a DM should do. Again, these classes are in no way intended to be balanced around "but you might lose your powers".
Further, I would go on to point out that forcing someone who plays a Fiendlock to be a right bastard and constantly act to further the goals of Evil in what is generally a heroic game where teamwork and trust are required to succeed seems at odds with what you'd want players to do.
It's worth pointing out that even the Paladin, that talks about fighting evil and doing the cause of good constantly, doesn't have "Must be Good" as a requirement. Nor does the Fiend Pact have "Must be Non-Good" stamped on it either.
That might rub some the wrong way, but it's intended to allow people to play characters without having straightjackets of "how you must play" imposed upon them. Evil can certainly have champions as well as Good, and the past of the game is littered with Anti-Paladins and Blackguards, just as examples.
And someone deciding to play a Paladin or Warlock or Cleric or what have you, that is at odds with the source of their power is certainly not powergaming by default! One can have a great story with someone who wrestles with the source of their power while trying to follow their own path.
Just as multiclassing isn't by default "powergaming", as I already pointed out, becoming a multiclassed character is a suggestion in the PHB for a "fallen" or failed Paladin!