I'm with you that the article is terribly written by an uninformed person (AI?). Of course Bitcoin had nothing to do with the ByBit hack. 

I'm asking whether is really preposterous to be concerned about a 51% attack. 

Especially when just two entities have mined over half the blocks in the last year. 

In my humble opinion yes. If you know anything about the hack it was due to human error. The thieves tricked the ETH holder. It’s not like they took a segwit address and found the private key via some magical hacking skills. ETH is very complex thus the attack surface is high. Bybit found out the hard way yet this article is blaming bitcoin saying it can’t be trusted because of this hack 