Remember that to be competitive, you want to get more zetas than your opponents. If the Devs double your rate of zeta "income", your opponents will also get double (or more).
If you want more zetas:
1) Get to the top of your fleet shard. Finishing first every day (and spending the currency on zetas) gets you 5-6 zeta materials per week.
2) Get Wicket & Mother Talzin to 7*. Their events recur pretty much monthly, and usually yield a total of ~6 zeta mats per month.
3) At the top level of the fleet challenges, I don't know exactly the numbers, but I'd say on average players could expect at least 3 zeta materials per week.
4) Join a guild that's competitive in Territory Wars. IF your guild wins 3 out of the 4 wars per month (and your guild is above 120M), then that's 11 zeta materials per month.
So at that rate: 20 (fleet currency) + 6 (Wicket/Talzin) + 12 (challenges) + 11 (TWs) = 49 zeta materials per month.
The "imbalance" in zetas has nothing to do with how available they are, and completely relfects how effective players are at collecting the available zetas.