I’m just thinking of it as a way to flesh out the game more, like they did with the structure damage resistances.
And by tweaking those values, they have another subtle way to nerf or buff weapons against specific counters.
What would make the most sense would be a mixture of resistances, like they did with structure.
It’s not a game changing idea, just another layer.
My logic on grenades and missiles was that maybe the weapon designers would build in some explosive resistance to protect against self damage and exploding ammo packs. Same logic as why melee would also have some explosive resistance (since they’re designed to rip into cars full of explosive materials, you would assume their designers would compensate for it).
It would just be nice if resistances had some logic, as well as being useful against some of their counters.