Fighting an aggressive "Gym Tyranitar" GRB-feeder for 2 hours

Earlier today, I was taking down a Mystic gym, where 5 defenders have already been there for 8 hours 30 minutes. When I finished the 2nd round, I was shocked to seel all the defenders at full motivation again. It was about 6pm, there was no good reason for them to be feeding berries.

I continued attacking for an hour. I always attack "Gym Tyranitars", my funny term for overstayer berry-feeders, non stop until I can't go on anymore. I didn't use many potions, as the gym composition was:
1: Chansey ZH/HB
2: Dragonite DT/H
3: Flareon E/FB
4: Gyarados DT/HP
5: Ttar IT/SE
6: Blissey P/DG (2.5k CP)

I kept attacking the Chansey non-stop. But the feeder didn't hit the berry cap, they fed 15 berries in 30 minutes.

Then after an hour, I went to attack a nearby Valor gym. I encountered some resistance from berry feeders too there, so I came back to attack the Mystic gym.

This time, the berry feeder wasn't paying enough attention. I took out the Chansey, but later they fed the Dragonite and Flareon.

Again I went on for another hour, and finally they stopped feeding. But I got sniped by Valor.

Luckily Valor only slotted in one Hariyama, so I managed to take it down very quickly before other Valor players slotted in.

Edit: I was also very close to gold badge for that gym, so that was another reason I kept attacking. I got my gold badge about 30 minutes after returning from the Valor gym.