Right now, with the current end-game encounters (ToC/ToGC), tanks don't really need to deal with trash. It's all purely boss tanking. Top single-target threat lets your DPS go wild without worry of pulling from the tank.
On top of that, most, if not all of these bosses, deal huge amounts of damage that are not physical, thus cannot be mitigated by armor. It can only be fought with stamina stacking. Self-healing also helps in encounters where casters (thus healers) also need to be mobile to survive.
Not saying that blood is better than frost. It's still a matter of preference, play style and maybe also depends on the encounters. Go with whatever you're more comfortable with and with the one you're more skilled with. I personally still tank as frost but in the process of learning Blood.
Self-healing. Really. It's there, it's hidden and it makes a TON of difference on how you or your healers feel about survival. I also find blood cooldowns more balanced & useful overall. I've tried both. Blood also has a much easier rotation so you can concentrate better on your surroundings. I absolutely LOVE frost spec, both for dps and for tanking. But i finally gave up & specced blood. Made my life easier.
I have recently switched from frost to blood, and I LOVE IT
Frost is nicer for AoE at first, but after you take a closer look, blood is awesome with hearstrike clave effect. What's more important, is the cooldowns. What Frost offers is: Howling Blast (10 sec cd almost killed this ability for me it used to be awesome, now since you can use it aprox 2 - 3 times a fight it's close to useless) + Unbreakable Armor (which is worthless tbh). If you compare it with Mark of Blood + Vampiric Blood + Rune Tap + Hysteria (put Hysteria during Blodlus on your best DPS and you will se his dps skyrocketing) the choice is simple.
The self healing component requires a lot of practice but it has huge potential and looking at my current experience it might be gamebreaking (VB + Smart Rune tap + death strike will net you HUGE amount of health).
I suggest you try Blood for some time, I have tried 2 times and each time i went bak to frost, but last time I gaive it a bit more time and it was worth it.
If you're only able to use Howling Blast 2 to 3 times a fight, then you either don't use your Rime procs or you don't have talents in Rime at all.
Saying Unbreakable Armor as straight down worthless needs rethinking. I know not all boss fights are purely physical, but they're not purely magical/bleed as well. Even for the current end-game encounters. With fervor of the frostborn use effect + black heart proc + Unbreakable Armor up, I'm able to reach 48k armor netting me 75% damage mitigation, not including the 10% (8+2 from talents) damage mitigation from Frost Presence. Whatever damage that we can't heal back, we make up for it in terms of mitigation.
Both builds are good and both builds have their pros and cons.