2) I didn't like that way. Shadows are squishy and you lose some time skillswitching which is crucial in Duncraig/Fauztinville, for example. Sure, necrobots/necromorbs will always take less damage, but that's why you have Dragonfire Oil and/or Punisher procs - to finish physical immune monsters

3) Yes, exactly.
4) Compared to a random/shitty Doom ammy - yes, compared to a +4-5 skill, Doom+TTAD, flat life/resists (and a lot of MO space) - no.