Having tried the 1 strong + 2 normals on ilum, I end up with around 80% life.
This is, however, when I don't use any of our cc (no spike, no stun, etc).
It is probably just a stuff problem you have.
I think you should try the 23/0/18 build first : the instant whirlwind will -definitely- change your life. Strongs do hit for a lot of damage when you just got 50 : they hit even harder than elites, and as a tank you don't have the burst to bring them down rapidly to compensate.
And, as our defenses are random, sometimes you'll just get hit by almost everything, especially at first, whereas a dps will always hit harder.
As you pointed out, you will definitely feel a lot tankier with the healer pet, because we are advantaged on long fights. That's however, quite frustrating sometimes : as you said, you will go a lot faster with a good dps spec. But in the end, with a dps pet and you with good stuff, it'll even out.
Anyway, that's the key for strongs : cc them if you can, don't forget to assassinate when they're under 30%, don't refresh wither/discharge when he's the only one standing.