Please don't misunderstand me. I'm not trying to be contrite. I'm just trying to make it fit within the lore I'm familiar with is all. I love the lore and history behind the series as well. If you want a comical take on things you should try watching Rune Soldier Louie. It's an interesting look at life on the Continent of Alacrast. I'm rather looking forward to playing in this setting. 
No worries. I am all for talking about expectations, lore, and all that jazz before we actually start the game, least we discover later that we are coming at this from different directions.

I did watch a little bit of the first episode of Rune Soldier a few day ago and discovered I should rather not watch the series right now, as it would seriously distract me from the slightly more serious tone I am looking for in this game.

When it comes to the Paladin I am all for it. What makes the Paladin special is that he dedicates himself to a quest. That could be anything from a priest of Myrii to a Holy Knight of Valis to a seriously dedicated fighter type (in many ways I see Parn as a Fighter who multiclasses a little bit to take some of the Paladin abilities because he is a non-magical fighter type at heart, but dedicates himself to a given task to the fullest).
When the Dungeon World rules say "Paladin" we can approach that in any number of different way. As far as the rules are concerned it may mean one thing, but when it comes to the character the door is wide open to interpretation.
I will not base this class on any specific lore - I will base it on what you make of the general idea and on what we agree on. A fighter with clerical magic, a cleric with good fighting skills, someone so dedicated to his quest that his sheer force of will grants him some magical abilitie? All that and more is possible.
Though I was kind of curious. I'm guessing that you are basing the use of paladins off the idea of manga Lady of Pharis? It was the only time I know of that they allowed priests to pick arms to fight.
Etoh does smack a Goblin over the head when he and Parn assault the goblin cave near Saxon. And I see nothing in the anime that expressly states that priests are forbidden to fight. I'd say a priest of Falis can certainly fight if it is for the defense of the greater good, and a priest of Myrii will also be allowed to do it, provided he follows the precepts of the faith (see above). A preiest of Marfa might be somewhat more limited, but I can still see them taking up arms at the very least to defend themselves.