Warmaster Horus
Explorer
It's a fantasy game. As a DM I would extend fire resistance/immunity to smoke just so I don't have greater devils choking on smoke in their lakes of sulfur and fire.
If a creature is immune to fire
and lives in fire...and smoke
and is always surrounded by fire...and smoke
and doesn't have a literal 'smoke immunity' in the stat block
...
(logical conclusion goes here)
smoke is treated as poison for the purposes of the game
Nah, the logical conclusion is:
The game holds many many abstractions. Hit points. Saving throws. And resistance.
If it lives near lots of fire, it can handle smoke.
Can you cite where that is in the DMG or PHB? I can't find it in the rules.
(This is rhetorical; it isn't there. You're house-ruling.)