Last but not least
I think I’ve talked about all the boys except Mikey… And I’m going to talk about 2012 Mikey specifically. I don’t mind that he’s not “smart” because I think a lot of kids can identify with him, they see themselves in Mikey. They might not be the biggest, smartest, or strongest, but they can still make a difference. And Mikey has saved the day many times (despite his mistakes). Just to name a few examples - Parasitica, Squirrelanoids episode (I cannot remember the name!), Dimension X, Kavaxas arc, Creeping Doom, etc.
Also aside from Leo, he’s the only other one to have successfully led the team. (Donnie seems to have little interest in doing so and Raph freaked out when he realized he had to put his brothers’ lives at risk.)
Mikey has also been right first about lots of stuff. He was the first to realize what the Krang were. The first to really try to befriend Slash and give him a second chance, same thing with LH. He knew what was going on with April and the crystal. He understood what Leo was going through in space.
I could keep going. But my point is that even though Mikey may appear “dumb” in 2012, if you look at the evidence, he’s far from it.
* Oh and he totally snuck up on Leo when he tried to go into the Foot HQ solo.