Get Reck by BPC. Get rekt by Shamblings. Get reckt by Living Infernos, or by Halion. Sure thing, your call. Gets those two vindication, period. It has a virtually 100% uptime. Logs support it.You can safely spend those 2 points elsewhere for a 25 man.
Last Word healing increase is of the order of 5% for small heals (Earth Shield/PoM) and below 2% for larger heals (LHW, HW, HL). Mithios NM is a flat 1.58% avoidance, and you know well that this is over a 20% decrease in the chance of getting 3 hits in a row, and that alone is worth a great deal. So no. Last Word is not a good weapon for survival. Divinity is a talent point that you can take without sacrificing any other avoidance/damage reduction talents, Last Word is a huge sacrifice in survivability if taken. Big no-no there.
You mention yourself the 'hidden' caps in resistance. The magical values that guarantee better worst case.
The AM being broken is that if two or more players are using the same aura at the same time, and one uses Aura Mastery, he cannot guarantees his AM will be affecting anyone but himself, because he may not be the one providing his aura to other players (since two or more players are assumed to be on the same aura). Most likely inintented behavior, when he uses AM he should provide. It is currently not the case. Watch your Shadow resistance while under your own Shadow Aura when another paladin uses Aura Mastery on Shadow Aura too, you'll see.