Yes, I know that you do not see anything wrong with that picture. The top 6 companies have 60% of the hashrate. What could possibly go wrong? As long as there is sand around...
Yes, but you would be saying the same thing if it were 10 with 60% or 20 with 60%. These are pools, miners can re-direct their rigs anytime. They are not going to conspire to destroy BTC, what would be the point.
To be fair it isn't really known how much of the hash rate is concentrated with a few large farm owners. The pool charts JorgeStolfi (or cypherdoc) likes to show don't indicate that at all. A single farm owner can split his hash across pools and a pool can represent hash from a number of miners. Both are unknown and unknowable. It is fundamentally a more dangerous situation than the first round of 51% pool scares when it was pretty clear that each pool had a huge number of independent miners.