Zeta Mats (Fleet Shipments vs Ability Challenges)

I drop 50 to 90 spots a day (while upgrading my ships) regularly. Maybe you're on a less competitive shard, I don't know. I think you're minimizing this.
You also have to remember, that after the initial ship upgrade grind is complete, these people can then spend on Fleet shipment Zetas AND run the 2x weekly challenges. So after that first 68 days, they'll have the advantage over you. They'll be accumulating zetas faster AND they'll have a stronger fleet than you.