Sybil is an attack vector against any crypto not just Dash, and I think Bitcoin will be the first target, because miners are already doing nefarious activities, like the backdoor meetings in Hong Kong or whatever.
I would not trust them the least, and they have the resources to mount a Sybil attack.
Yeah sure it is, but your missing the point completely with dash. A Sybil attacker in Bitcoin does not have much power at all - they still would need hashrate to do anything.
With dash, there is the economic fee of locking 1k dash for becoming a node representing quasi-stake. This fee is so trivial, especially to actors who were able to acquire a large amount of these tokens for "free". The low expenditure of value required coupled with the power of masternodes is absolutely ripe for masternode collusion and centralization.