I've had trouble with warlocks all through 5e, and I could use some insights from other folk. Maybe I just need the discussion.
I've been playing and running since AD&D, so I have solid ideas of what the strictures of a cleric and paladin should be, where their powers come from, and the responsibilities of those classes. In some ways, they're still baked into the class, even if 5e has handwaved a lot of it away. But Warlocks, as they are now, are a 5e construct.
A paladin's power is drawn from their oath, their faith (in that oath or deity). I still ask paladins players to pick a deity or something in that vein.
Clerics get their powers from their deity, their faith, etc.
Warlocks, according to their 5e14 class description, get their power in exchange for performing services for their patron.
Here's one hurdle: the warlock actually gets their power by leveling up- whether it's experience points or milestone leveling, the warlock doesn't need to be doing anything for their patron to "gain power." You could say similar things about clerics and paladins, but a paladin just has to keep to their oath- a cleric just needs to adhere to their faith. If they violate those, then there's trouble; class changes, power-stripping, the kind of stuff that doesn't actually happen at most tables but the mechanical suggestion is there, both consequence and requirement.
These rules were removed from paladins for a very good reason. Those being that they actively encouraged bad DMing and negative play experiences for the players. And the cleric and paladin
actually get their power by levelling up. Warlocks are no different here.
Indeed stripping powers the way you indicate is bad storytelling and blocks off plots. For example you actually can't really have a corrupt paladin.
"Sir, we have reason to believe that one of the paladins is ... a traitor."
"You know the drill. Get everyone down to the courtyard and we'll see who can no longer lay on hands"
And the old school Paladin codes of conduct in addition to that were mostly used as "gotchas" by bad DMs (something that was particularly bad in the 2e era when paladins would lose their powers if
mind controlled into committing evil acts thus making this smart in character villain play to break paladins). What the old style rules meant is that a corruption arc became impossible because it was "bam! you've fallen" so Paladins basically needed to behave like jerks with iron rods up their backside lest they do one single thing the DM considered an evil act (and I know that Gygax and I have very different opinions on what is considered evil). So the Paladin falling mechanics were toxic to roleplaying complex characters.
It's also worth mentioning as an aside that at least under Catholicism once someone has been ordained a priest the change is permanent; they are always a priest; not stripping precedent has
serious precedent in the real world. Instead the controls are through dreams and through consequences via the other members of their organisation (or other organisations).
Power stripping and DM fiat class changes aren't mechanically there
even as mechanical suggestions in 5e and consigning those suggestions to the dustbin of history has been a significant improvement to the divine classes in 5e over classic D&D.
Yet I write all that and 5e has the
best potential paladin falling mechanics of any version of D&D and it's not even close. This is because you don't take away the powers and leave them as crippled or utterly change them. Instead you change the
subclass. Switching from Oath of Devotion to Oath of Vengeance is a much more nuanced change than Paladin to Blackguard while changing less but in the right places. (And a big part of it being the best is it's not an actual punishment for the player and is something the player can accept).