I'll offer a differing perspective.
On my Juggies, I usually stay Immortal all the way and go all tank gear (as much as possible). I use Vette and Jaesa all the way up and keep them geared at least as well as I am.
I keep aggro on everything and Vette/Jaesa absolutely rips the sh*t out of everything. Tends to go very quickly and very smoothly, and I have to do very little Channeling between groups, if any. Maybe every few groups I have to do a little.
This,, yes. Immo spec doesn't even do bad damage. I have different rotations for what I want to accomplish at a given time. Can go super-tank and be about invincible, or go dps(ish) and still be really tanky and dish out some dps. All in the same spec, depending on rotation.