[Oberon] has a few offensive and defensive buffs in his kit. Most of them support other frames more than himself. We subsume an additional buff to play to this build's strengths.
Elemental Ward and Warcry give you hybrid offensive/defensive options but are a bit weaker overall. Element buffs like Nourish and Shock allow you greater freedom in your weapon loadouts but may require augments or build tweaks on those weapons. Roar, Eclipse, and [Xata]'s Whisper give you the strongest damage buffs but have certain drawbacks due to balancing decisions limiting their output.
Roar is chosen because it's the strongest buff in most setups. Elemental Ward and Warcry are good for survivability. Reckoning is replaced because it's a weak and expensive ability on this build.
Strength is extremely high on this build as it attempts to give as much damage as possible against enemies that are immune to armor stripping effects. If you run more defensive subsumed abilities you can drop [Blind Rage] or [Transient Fortitude] for more Duration and Efficiency.
[Constitution] or [Streamline] can be replaced with more Range if want an easier time hitting allies with the buffs.
[Phoenix Renewal] can be run over one of the flex mods if you're having issues with survivability.
Arcane [Guardian] provides a large boost in survivability. It can be replaced with any other arcane to suit your playstyle.