Conceptually separate breath weapons from rays, making them not trivially reflectable. Make it possible to suffer reduced effects from a breath weapon, with the size of a worn shield a factor in that reduction.

Possibly make dragon armor of the same type as a given breath weapon (e.g. red dragon armor versus fire breath) reflect that breath weapon, and only that one.

You can use #monster while riding a steed with a breath weapon to make it use its breath weapon. You get prompted for the direction.

Kicking a dragon while you are riding it as a steed makes it use its breath weapon (if it is currently able to, with its cooldown over). This is still subject to possible tameness penalties and other side effects of kicking a steed. It’s not defined whether the player should control the direction it breathes in or whether it will select a target itself.