You don’t need “several answers”, you need the potions Brann provides specifically to handle the fact mobs are intended to hit you in a delve.
I would only use my pet if I specifically need to separate mobs or tank a rare elite. At low ilvl where a pet would help me survive, it’d go down to autoattacks or struggle to keep aggro. At appropriate ilvl, it’s not worth the extra time from less damage. MM toolkit, without pet, is more than sufficient with the proper Brann spec for solo delves, and that’s all there. All the toggle changed is that, if someone does want the option, it’s now there, effectively for the RP or legacy mobs that need to be separated.