So, I'm not 100% sure of the order, though it shouldn't matter in the calculation. The sequence is roughly this after the hit has passed the hit table as a 'hit', i.e. avoidance didn't work.
(Unmitigated dmg) => reduced by armor % (well-geared tank will be around 63-65%) => reduced by Frost Pres % (5% base, 6/7% with improved pres) => reduced by Blade Barrier (5% for full 5 pts, assuming it's up) => reduced by Grace/Vigi/BoSanc/etc (3%, if applied) => reduced by proc/ability such as IBF (35-50% depending on glyph and Def)
Each of the % effects is applied after the next, so it reduces with a diminishing effect for stacking multiple dmg reductions. In other words, if your armor reduces physical dmg by 60%, and your IBF reduces it by 40%, you won't take 0 dmg.
So, for a quick real number example. Hatefuls are about 55k dmg unmitigated. We'll say you have 65% reduced from armor, and Blade Barrier up, but no other effects.
55k unmit => reduced through armor to 19.3k => reduced by Blade Barrier to 18.3k
Without Imp Frost Pres: reduced by Frost Pres to 17.4k
With Imp Frost Pres: reduced to 17k
So those talent points in this situation saved you ~400 dmg per swing. So I'd say the talent is a major yes for survival value.
If your PS is about Bladed Armor vs 2h Spec, we can look at it point for point.
1 pt of Bladed Armor is 1 AP per 180 armor.
1 pt of 2h Spec is 2% weapon dmg increased.
For a moderately geared tank their armor is say 28k and their weapon dmg (base dps + AP/14 * weapon speed (normalized at 3.5)) is at base about [203+(AP/14)]*3.5. We'll say without either they have 2000 AP, so that weapon dmg is 1210.
1 pt of Bladed Armor is 156 AP, which will increase that to 1250.
1 pt in 2h Spec will increase that to 1234.
Here's where Bladed Armor wins even further: 2h spec will increase weapon dmg and trickle down to your strikes (anything based on weapon dmg). However, Bladed Armor increases your AP which increases weapon dmg AND is applied to most of your spells through an AP coefficient, so it will also increase IT and HB damage for Frost. It also increases your disease damage.
Bladed Armor, as a tank*(as DPS it's more of a balanced talent), is one of the best, most universal dmg/threat buffs you can get, bar none, and regardless of spec.