I think we should need specific items that let us dip our weapons, not just random surfaces or candels. In you put a sword in a campfire for a couple of seconds you are not going to have a flaming sword, just a sword with a bit hotter blade.
If instead we need one action (or bonus action) to use an oil flask on our weapon and THEN another action (or bonus action) to dip said weapon in the fire it would make so much sense and would be more balanced.
