To be honest if Gorosei are all yc1 lvl, it won't make sense that WG has that insane power. Admirals are like yonkou so + VA + Seraphims + now if gorosei are King or ben beckman lvl is too crazy to be believe.
Seraphim could be End game material if they become mature and more experienced.
You will have:
Luffy PK/PK+ level
BB PK/PK+ level (if he joins them)
Zoro PK level
Law Top Tier
Kidd Top Tier
Sanji Top Tier
Maybe other Top Tiers helping the alliance
Some Strawhats being inbetweener or even Low Top Tiers
Other powerful allied members
Wano alliance
Elbaf alliance
Revos (Dragon, Sabo, etc)
Maybe Cross Guild helping them
Enel Low Top Tier/Top Tier
Other allied members
Then you have the WG + navy. There are simply too many Top Tiers on the good side. 3 or 4 Admirals + 5 YC1 level characters ain't gonna cut it.
Also, I doubt the entire war will only happen in a single arc. And if Admirals are defeated, the WG basically has no chance against the alliance. Luffy and Zoro might even solo them if the WG is just a bunch of High Tiers. Seraphim could grow stronger but again, the alliance has so many heavy hitters, I doubt the Seraphim will be a huge threat against the good Top Tiers.
Sure, someone like Imu could make the difference if he's the God Tier of One Piece, easily destroying Top Tiers from left and right but until Imu does his move, I think the Gorosei will have their turn at first. Similar to Skypiea arc.