TLDR you need to get your gets to 45% def either through raw defense stacking or -tohit debuffing
Softcapped pets are happy pets. There is nothing better for you as a mastermind to do than getting your pets softcapped however the hell it is possible.
/radiation has some very small ass radius on their debuffs. I believe it is only 15ft. and if i am right on how i think radiuseses work, thats melee range all around your anchor. 7.5ft in all directions. check other radius from other sets to see how small radiations range is. dark and trick arrow are worth noting
Some masterminds require expensive builds and level 50 with a firefarming account powering you to max level. Cytoskeleton hamis in Enforcers can bump them up to 20-24% def to all. thug-cold/trap/dark/etc shines super hard when your enforcers are giving off a ton of defense working with your buffs or debuffs. on the flip side, if you go thug/ff you will be way over defense softcap and no snare/slow pit. every single one of the combos you listed do not synergize well.
Forget necro as whole or get some thicker skin while playing it. i tried necro/ff, necro/dark, necro/thermal and /ff only really works because of mace mastery's power boost bringing them to defense softcap. necros innate resists are rare damage types leveling up and hard to synergize with any secondary. i had to adopt team teleport on my necro/dark to really move that dark servant around with its gigantic -tohit aura. teleport target is also a thing for the servant
beast/nature reroll into beast/cold. adopt a tundra like avatar and go with it. beasts innate defenses with iceshields+fog+maneuvers is good times.
thugs you have so many things to work with here. thug/trick arrow to keep up the natural crap while still having flash arrow at level 1, glue arrow at 2 and the fabled oil slick arrow. thug/traps, thug/dark. i can go on but i already typed too much