You know, this rules seem kinda borked.
400 CR 1/2 dudes have 80 BR.
400 CR 1 dudes have 200 BR.
400 CR 2 dudes have 400 BR.
400 CR 3 dudes have 800 BR.
Since the RNG is a single d20, that means as long as you have a BR advantage of 20+, you simply can curbstomp any amount of lesser enemy units. And you only need 20 CR 2 or 40 CR 1 dudes to get that +20 bonus advantage. Numeric superiority is pretty much meaningless, and morale (which includes better gear) only matters when two units composed of pretty much the same power face off.
On the other hand two same high BR units with top morale can bash each other for hours before one finally crumbles (only need to make a DC10 morale check if you lose badly which you auto-pass with morale 9-10 and a one-time DC 15 at half BR). Which is actually kinda realistic given real world large size battles and can give you a deadline of "the elven royal guard can't defeat the demonic huruk-hai but they should be able hold them for X hours for you to mount an assassination mission on the uruk-hai general or something", which is some use at least.