You are releasing PVE content and hulls too fast - people find it more of a chore at this point. When you release new content, it should surprise people and get people excited. People shouldn't be predicting how your new content is coming out. Right now your new content isn't new - its expect AND part of the game. How the game works right now is that you release "new" content every X weeks. This is not new content.
But then you have the issue of stagnating the game when people build the new stuff and have no new things to build. Thats why PVP should be the main focus.
Instead of releasing new PVE hulls, make events release new PVP hulls, weapons, turrets, base upgrades (defence), etc.
Instead of adding new tiers to PVE stuff - where people HAVE to get that PVE gear or fall behind - make it so people get PVP stuff, and if they miss it - they lose their medals. Not be forced to coin back to pace.
Reduce the time to build and repair your PVP hulls. Like significantly. MOST successful RTS games have MUCH lower "PVP" times. That is; the times it takes for, example, to train new troops would be a ~1.5hours. Not 16 hours. In essence, repairing your PVP hulls is training your troops. Building your PVP hulls is researching/unlocking a new troop.
Obviously if this is the case, make bubbles lower to the minutes. Just remove base repairs honestly.
THEN give PVP a reason to do. Medals aren't enough. Make alliance play more fun/rewarding. Give people a reason to PVP instead of just medals. New/exclusive TOP Alliance medal skins, etc. Give people a reason to coin their PVP fleets. Or coin their BASE DEFENCE. You get the jist.
Slow down PVE a significant amount. Make PVP the center. Focus more on PVP and Alliance play.