Perhaps amusingly, what the tertiary and quaternary configurations give up for a third weapon is not additional speed and agility.
The coolant system would enable the Titan to draw an activated system immediately back to their hand rather than waiting for it to cycle through the Titan deck. This can give it the Titan a third limb or weapon activation as the timing allows. It also gives it another defensive option, to make up for all the block reactions it would lose with the third weapon and two arms.
This does require ripping out one of the capacitors, but where their optimal use requires the Titan to be using two-charge systems. That's only really the weapon systems, in the tertiary configuration, and the macro laser in the quaternary.
This isn't the whole solution though, as it occurred to me that the turret is one of the reasons the primary and secondary configurations are so effective. Being able to jump sideways seems like an equalizer, especially where weapons also get 270 degrees of fire.