Mostly agreed, except I read it as:
Marine HQ + Warlords > Emperors.
Emperors + Warlords > Marine HQ.
It is stated many times in the story, Warlords are part of WG(Like Marine HQ) by title, but they are still Pirates(Like Emperors) by nature, can not be trusted. They are a force that can flip against either side depends on the situation, and because how strong they are, it can be decisive. Even if not flipping sides, the Warlords don't care about the Marine HQ much when fighting along side them, this was clearly shown in MF, other than Kuma who's unconscious, every Warlord has shown to be either directly or indirectly damaging the Marine assets, causing them extra trouble.
In other words, Marine HQ can never rely on the additional power of Warlords when it comes to overpowering Emperors, therefore it creates an unique balance between the 3 Major Power.
Orochi's words hold no more weight than Pica claiming he can take care of Marines(including Fujitora) + Pirates(including Luffy + Law) using his DF power.