Berry-fed Blisseys impossible to solo?

Its pretty tough to beat a Blissey 11 times in 30 minutes. The actual combat time is doable but with the team selection and battlescreen there are a lot of wasted minutes. I'm don't believe it to be impossible, but very difficult. Especially since you have to manually choose Machamp Every time and he's never atop anyone's list.

Edit: to answer your question one golden berry will fully re-motivate Blissey. One player can feed one pokemon ten berries in 30 minutes.

If your area has high gym turnover, it is normal for players to feed berries when a low level raid is starting, just to get the guaranteed 6 coins. Especially for yellow and red teams.

You can feed your Pokemon remotely you know. A determined player feeding a 3000+ Blissey is tough to take down with only 20 minutes until the raid begins, add others feeding it spoofers or not to get the gym control bonus and it could be next to impossible in that 20 minutes.

Yes. A gym that is actively defended is impossible to take down regardless of whatever trick you are using.

I experienced that a lot when I was trying to attack gyms, where CP3000+ Blissey was the 3rd defenders. After knocking out the first 2 defenders with no heals, I thought I can quickly dispatched Blissey and the rest. But everytime I took it down to the final CP before getting knocked out, someone will keep feeding golden berry to it. Tried several times but same thing happened. In the end, after 10 or so minutes, 2 new defenders joined in at the 5th and 6th spot. I decided to leave and not waste any more time and potions to take the gym solo.