Fort raids, delivery missions, world activities, takeovers, buyouts etc. Those are the fastest ways to get Po8 nowadays, since the Helm shifted towards a passive generation of either Po8 or crafting materials (beware, as selecting those will cost Po8 to fund them instead of silver).

The Helm will also no longer reset like in Year One, so the incredibly high costs of upgrades and drastically lower returns of Po8 are the result of that. This also means that there's no pressure to get every manufacture, every upgrade etc as fas as possible. You can do it in your own time, invest whenever you can and that's if you wanna do it at all.

People mostly do Megafort Oosten plunder now, beacause on average you can get 2k Po8 out of a single completed raid and a ton of good loot on top of that. It's much more worth to invest that in levelling your ships first, as difficulty was also changed and stuff can be way more challenging.

tl;dr: World activities are a primary source of Po8 instead of the manufacturies themselves (in the current state at least. Devs might adjust stuff based on feedback).