Currently fire resistance stops a certain amount of damage from so called fire attacks. The logical problem with this is that a fireproof armor should protect you well against attacks that literally are based on fire (dragon breath, flamethrower, fire spells, incedinary weapons), not against attacks like flaming sword or arrow where fire is only a small part of the weapon's additional damage effect.

To fix this I propose that we split fire attacks into flame and fire based attacks.

What does this mean?

A burning sword or arrow is flame attack. It should inflict the healing penalty, but should not be resisted by the fire resistance or fire resistance should only apply in largerly reduced manner.

A flamethrower, firestorm, incedinary thrown weapon, dragon breath are fire based attacks as their ability to harm is based on the majority of the attack being fire itself. They should be resisted well by fire resistance. Obviously healing debuff still applies.

This solves the old problem of dragons needing to lose fire attacks so that they aren't too weak towards Chaos Dwarfs.

Why would Tyrion's blade or Phoenix's claws or beak be weaker against fireproof armor to an extreme degree?

The change is simliar to the old separation of the magical attacks and magical damage.