Split the Rangers into 5 man units. You gain little to no advantage from large units.
The DA gain nothing from having large units but also loose nothing. Are they going into a transport?
The guardian squad is fine if you have a farseer or warlock to stick with them but overall big units usually loose more than they gain.
Eldar troops are pretty good in the new book but there is no magic number to hit. Take enough fire power to kill the enemies troops and stop the enemy from killing yours. Then take enough troops to claim #objectives +1 but if you have enough killing power they can be wet tissue paper as far as durability goes.
I can see why breaking the 5 man squads would not be a terrible idea, but that does not make them any more reliable. I would think that makes them easier to pick off to be honest. and no I am playing footdar. so no vehicles short of war walkers