Gaming isn’t the only thing they do though, cornering multiple markets as one company is the definition of a monopoly. The merger was thoroughly investigated as to whether it would be unfair competitively, that is a different way of saying they were worried it was gonna be a monopoly, and in that case they were even only concerned about the gaming market.
I’m not just throwing around random terms, it is indeed approaching a monopoly. And could indeed be bad long term, even if it gets rid of kotick and helps clean up blizzard in the short term. And that’s a pretty big if.