Rather than merged I think they were simply bought by Activision. An Acquisition is when one business entity becomes a child to another, a merger is when the two become one different entity.
"Mergers" end up being acquisitions in the majority of cases. One company culture will prevail, one companies middle management will take over the administrative sides and depending on the structure also the technical side.
Okay but the merger was Vivendi Games who merged with Activision. Blizzard Studios was never at any point Activision's equal, they're a bought and paid for property of Activision.
I didn't even know they merged with Activision. And I didn't even know that the latter has also gone worse than I expected. Which is a shame because I have fond memories of pre-2010s Call of Duty games.