Honestly, just the numbers in the linked article makes a solid case for not opposing the merger even without considering Nintendo.

There are almost 2.5 times as many Playstation consoles as XBox. How could merging with just one publisher possibly catapult the Xbox past the PlayStation to the point where it creates "an uncompetitive environment"? If anything, I'm seeing that Sony is dominant despite Microsoft's best efforts, and anything that can bring them closer to parity can only increase competition.

Honestly, compare the amount of console exclusives on Playstation with those on Xbox. If Calll of Duty becoming an XBox exclusive will unbalance the market, is the FTC prepared to tell Sony, who already has a dominant position, that they can't keep making console exclusives?