Come on ppl, this is simple game on numbers

HUnters summon 70-100 lds units, they are 160 lds. So they summon 45-65% of their troop, and split their dmg in half with their summons, thets best part. Hunters are great tankers with this skill, with 20% basic physical res, and guardian medal.
Hunter get attack dmg is halfed with summon, is summon is attacked hunter take no dmg, but if hunter is under poison/burn every turn part of that dmg will be transfered with summons. This is important because they also have 20% poison res so that dmg will be lower then from burn, so if attacking enemy huters fire is better then poison to kill their summons faster.
And as for first question `Total pain` is what says every time hunters split dmg with summons, that`s skill name. Lds of summoned units doesnt depend of hunter numbers decresing during battle, but of dmg they split with hunters. So if 100 bears are summoned by 100 hunters, and you kill 20 hunters, bears will not lose 20 units, but they loss will be 50% of dmg done to hunters considering bear resistances. It`s a bit tricky to get this on start, but it`s all simple math

When dealing with enemy hunters best way to kill them is fire/magic dmg since they dont have res to it. If they summons somehow stay alive after hunters die (it happens sometimes) it`s because of resistances- if they summon fire dragonflyes hunters will die before them of fire dmg, since dragonfly have basic fire res . . .
If you play red sands or RSE mod, take in consideration that hunters will have exp and maybe higher res per unit lvl, but their summons will NOT, so hunter may have all res on 10% or more, but summoned troops have resistances as any other unit 1lvl.