Can zero-transactions block generation be called as a Sybil attack? Imagine a malminer with two important abilities: having enough hashrate for producing blocks in a single-miner mode in reasonable amount of time and having a malconfigured miner software which doing somewhat a usual mining job, but including no transactions in the block except of reward. It might be more productive (from malminer's point of view) way of converting a computational power into some bitcoins, because changing the nonce only looks much easier than downloading and ledgering the real-world transactions. Can I call such intentional easy-mining a Sybil attack?
Can I call such intentional easy-mining a Sybil attack?


No. Because mining is a memory-less process, it is quite possible that subsequent blocks be found while the mempool is empty. Furthermore, the idea that verifying transactions takes away mining resources is moot since the SHA256 hashing is typically done on specialised hardware that can't do anymore than SHA256 hashing, so verification effort and mining effort is mutually exclusive.