Up until now all opposed combat CGs have been exactly even in terms of final target and tier distribution.
This one is a bit different because it's more closely tied to a story than the previous ones have been - essentially, the Marlinists are one system against the might of the Imperial Navy, so they have a harder task to defend the system long enough for their transports to escape than the Empire do to enforce the blockade. On the other hand, the Marlinists get a partial victory at Tier 3, whereas the Empire has to get to Tier 5 first to stop them getting that partial victory.
This also has the consequence that the relative efforts match a lot more closely to the supporter numbers on both sides, keeping the final result unclear until the end ... though it looks like the Empire might just have a slight edge - whereas the numerically even ones have generally been obvious walkovers a few hours in.
It's a bit of an experiment on Frontier's part, I expect, but it seems to be working.