The ultimate level of "influence in the network" is full control which requires more than one account. It wasn't just creating multiple accounts that made this a Sybil attack. As you've already mentioned, Steem has fairly good protections against that attack. It's the combination of stake and creating multiple pseudonymous identities which made this attack possible and that is, to me, undeniably a Sybil attack. I'm confused why you're stuck on this point because multiple pseudonymous identities was clearly required to pull this off. Those accounts were not real people. They were one person pretending to represent 20 different entities. DPoS is designed to have individual block producers, not one producer pretending to be individual block producers. These 20 accounts may be running in the same datacenter or even the same server for all we know!

From: https://steempeak.com/dpos/@dantheman/dpos-consensus-algorithm-this-missing-white-paper

Under normal operation block producers take turns producing a block every 3 seconds

How is it "taking turns" if they are all the same person in control because of this Sybil activity pretending to be multiple, separate accounts?

The DPOS algorithm is divided into two parts: electing a group of block producers and scheduling production. The election process makes sure that stakeholders are ultimately in control because stakeholders lose the most when the network does not operate smoothly. How people are elected has little impact on how consensus is achieved on a minute by minute basis. Therefore, this document will focus on how consensus is reached after the block producers have been chosen.

The election process failed because exchanges don't have skin in the game. They didn't vote with their tokens so they don't care if it impacts the token price negatively.

I think this document didn't spend enough time on the election process as that's where this Sybil attack became a reality.