then I noticed: I don't get it, why the change? Was it cuz Optimus couldn't fit up there? Seems kind of unlikely. This and the red convertible that moved in DotM during the Mexican standoff.
The red convertible could of been put in reverse and moved a bit. There where people inside of it still. Look at the screens. they are ducking down.
Most likely they were omitted so we could clearly see Prime hook into his face. I have no idea how the right one regenerates there
.....ffffffuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuu
Well, Grindor isn't the exact same model as Blackout. That's concept art of Blackout you're comparing Grindor to as it is. He's a retool...ish of Blackout. He's not the same.
I'm guessing the regenerating air intake is an animation error. Gets destroyed early on but they forgot to keep it that way. Not sure about both disappearing only when Optimus is standing on Grindor. Perhaps quietly left out so Optimus could actually stand there, the animators hoping no one would take notice. Of course since they were already destroying those things they didn't really have to rely on visual tricks. Also, the entire rotor system vanished for Grindor's death. Grindor has a (slightly) different alt mode, but there's no indication they edited the actual CGI model. Besides, we're focusing on the air intakes, which are the same on both.