that's why i was using that example to show where his logic falls apart. for the same reason a hammerdin would obviously not optimize for magic immunes is the same reason a lightning sorc should not optimize for lightning immune. the immunities are a low % of the monsters, and killing them 20% slower will still net a much higher killing speed given that every other monster is killed 3x as fast
There is only one magic immune mob in the game unless you go out looking for the one-off variants in niche zones, just unravelers, who hammerdins can already kill with holy bolt + merc.
Lightning immunes are found in just about every zone every act, and most monsters have a lightning immune variant, and many uniques that aren't natively immune become so with lightning enchanted, others with magic resistant.
Rogue archers, axe rogues, spear rogues, claw vipers, vampires, urdars, baboons, bats, hawks, storm casters, death brawlers, council members, blowpipe fetish, unravelers, leapers, abyss knights, scarabs, skeletons, saber cats, skeleton mages, slingers, quill rats, succubi tainted, vultures, souls, zombies, zealots, cantors, even flying scimitars that pop out of traps and whomp you on the ass.
What do you do when you are against a TZ96 P8 Tier 5 herald with 2.4 million HP and light immune with 14 light immune minions, dealing 850% damage himself and 150% per minion?