with ships PVE I farm all my ships from there and spend every single last bit of fleet currency on zetas and I make the lowest amount a day possible (800), so thats 1 zeta every 3 days, but then I have the fleet challenge complete so I collect zetas from there if RNG is kind to me (today I got 2), and then from login and TW...etc I can get roughly one full zeta a month which is not so great but will increase over time.
Not all ships are in the PVE battles but I got them to a point I dont need to farm them and while I work on my ships I can farm zetas and it will slowly increase as my ships get better.