Does anyone else think 6 Pokémon instead of 10 is a problem.

Yup. I only need 2 pokemon...Dragonite sweeper, Blissey to finish the job.

Did they say 6 somewhere?

I don't think it'll be easier. It'll definitely be more fun. Before it seemed easy taking down 10 because if you had 3 gyarados in a row you can easily take it down with a jolteon and still have 5 others to use for the rest of the gym. But that isn't the case anymore. Can 1 dragonite really go through a maxed out steelix, snorlax, blissey, cloyster, slowing and lapras? ( I picked these for example only). Those are good defender mons with great defense. Now their lower cp isn't a factor in holding them back from really shining as defenders
With the diversity in gyms now we won't be able to sweep through so easily because of type advantages having a larger effect now as well.
I could be wrong and yeah maybe 1 dragonite can sweep through if the defenders aren't maxed but knowing most of us we will Max out our defenders with all the dust we have been saving these last few Months.
I'm hopeful for the changes though. It seems fun.

Counter: What if they introduce dodging for Defending pokemon? Still so easy?

Niantic clearly put a lot of thought into this. They know that most good players have plenty of Pokemon that can take down multiple defenders. I think there are other things we don't yet understand about this...