The default black hole gear isn't well optimised for some classes as you obviously know, but if you're in Rakata the increase in armouring and hence survivability means trading up for BH is still a good option, even if you stack more endurance and less of your main stat. I consider it an acceptable transitional phase while you're building up credits and comms for optimised armouring / mods, or running ops to get campaign gear, and it should be more than good enough for TFB SM.
My scoundrel healer has 23K health in augmented Black Hole gear. I've left the Rakata implants in because they're better optimised and have no armouring bonus. Whatever augs you go for on a scoundrel, you stack yet more endurance, hence more HP, but it's a necessary evil.
Now, what makes me really laugh is tanks with 30K HP upwards. You don't stack that much endurance with regular gear, you have to deliberately optimise for it. The only way to do that is to neglect other things. Invariably when I see one - and they're rare - their defense, shield and absorb are absolute pants. Any tank with over 27K HP in the current gear available makes me very, very suspicious that we have an idiot in our midst.
Your last paragraph is a little off. Dread Guard tank gear is extremely endurance heavy, with very little sacrifice in the mitigation stats. My shadow tank has 29k hp with 26% def., 65% shield, and 60% absorb. it's very easy to get over 27k with full mitigation stats, as long as some dread guard gear is in there.