Roar grants you enough damage that you can turn [Rhino] Stomp or some of the subsumed abilities into competitive albeit expensive nukes. We subsume a nuking ability or something that allows [Rhino] to support another nuke frame.
Breach Surge is chosen because it effectively doubles the amount of kills that you'll be getting after killing enemies. Roar double dips off of the damage and a good team can create a composition where the sparks can clear the entire map. [Garuda]'s Seeking [Talons] is a great example of one of these synergies. Expedite Suffering is another good option in those scenarios but it requires some form of energy support like [Trinity].
[Rhino] Charge is replaced as it has no purpose in this build and we have enough range to use [Rhino] Stomp in emergencies.
Efficiency is at the minimum possible as this build is usually run in teams where you have an additional frame providing energy. If you're having issues with your energy economy you should replaced [Blind Rage] for [Augur Secrets]. Realize that this greatly reduces your damage. The polarity plan doesn't really allow many other options.
[Energy Conversion] is mainly used on Roar and shouldn't be too much of a burden in most content.
[Rolling Guard] protects you while you're recasting your Iron Skin or if you happen to be nullified and need some time to think. [Iron Shrapnel] is another good option but might have issues fitting into the polarity plan.
Arcane [Guardian] synergizes with Iron Skin but can be replaced with any other arcane to suit your playstyle.