I've tried buying more allies and getting more buildings and replacing older stuff like guilds for better stuff like strongholds but I'm still not getting any increase in plunder per hit on eb
When upgrading guilds to SOS you may see a drop in plunder at first but after you get a few and start upgrading them you should see it raise up. When testing your plunder look at the ally plunder stat as that should remain constant no matter how many troops you have.
You already got ~1.6T in allies. You will be in Max Plunder until Build Complete, or close to it any case. All you should do now is just upgrade buildings. For efficiency: Don't upgrade Highlands/Hoarfrost above lvl2 and don't buy more than 15 lands of either. Rush to Abyss and OR, that's where the real stats and plunder per gold are