Thanks for the take on the writers. Yeah, without acts 2 & 3 we can't see the pay-offs, therefore it is indeed just conjecture.
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The lie is a big deal for an oath taker. (Really it's a big deal in of itself, I never never feel good about it.)
It's an attack on truth and it chips away at the foundation of an honest character.
The Oathbreaker has a different kind of challenge before them. They no longer have the difficulty of walking a declared path, rather they have the difficulty of needing to forge their own path of nuanced 'if' statements. Gosh, when I give this a play through, I'll need to have pencil and paper ready to write what I do under certain circumstances, and why.
I like the shining knight archetype, and for me that's enhanced by having a consequence (temptation!).
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[Actual play through experience]
My MC picked the dialogue line tagged with [Paladin] and [Deception] where I tricked the Tieflings into letting my party deal with Lae'zel, and they then go elsewhere.
It's tagged hard deception, but really it's a truthful mislead that serves the good of all. It is true that my MC will take care of Lae'zel; under MC leadership she won't harm innocents and MC has a lot of reason to think Lae'zel has a path to the cure, therefore saving the life of self (legitimate value). The dupe also saves the lives of the Tieflings who have an understandable but ignorant reason to kill Lae'zel. Allowing them to do so would in itself be supporting the lie that all Githyanki are evil.
Long story short. Paladins in good standing don't lie, but they don't have correct misunderstanding, particularly to would-be killers.