Twisted? Magical weapons dealing additionnal damages are a part of every DnD video games (and they are in the DMG). Dipping a sword in a candle is stupid and only exist in BG3.
Yup ... twisted.
Im affraid i cant explain this properly, nor i see any reason to ... in my eyes its just odd, but that is not important at all ... what matters is that you are happy with your game.

Just a question tho ...
Lets put candles aside, and ignore any other source of fire damage, even the logic that with some kind of oil it would totally be possible for short period of time ... but how about poisons?
They are also "part of every DnD video game".
That's not how Unarmoured Defence works either in practice or in theory. Helmets are not armour in any way that matters.
I dunno its just bugs me to be honest ...
Either they should remove the Armor property from the item completely, since it does nothing anyway ... or they should include it to all things that matter.
That is simply how i see it.
Including Gloves, Boots, Helmets, Belts and every other possible item ... if you are going to ignore any of those properties, what is reason for their existence? O_o