False, it depends on the attacks used by the boss. If it's using M/R E/K attacks defense will have less value since an attack that gets trough the defense will be mitigated more by armor and shield, but if it's using M/R I/E attacks each defended attack will provide more damage reduction.
That's what's messing my calculations up at the moment - I want to optimize for Kephess, but I'm not sure what his balance of attack types are, so I'm going with the optimal values assuming only M/R E/K and then arbitrarily raising defense a bit when I mod my gear.
This is total hokum. There ARE no M/R I/E attacks in the game at present. If there were, it would indeed slightly inflate the value of Defense, but there aren't, so it doesn't. In its absence, the repeatedly-calculated ideal mitigation values remain as the stat split which minimizes mitigate-able damage taken.
Kephess is easy. All of the big spike damage hits in the entire fight except for Rail Shots on the Pulsar droids are yellow damage (Empowered Slash + Savage Wounding, Rocket Blast). The bulk of the damage you take is from Kephess' regular melee attacks, which are just plain Jane M/R.