*you're

Yep. I think you're bang on in this case

The show sucks though. The song is catchy but the show is pandering and knows that its base will lap up anything crapped out with the ninja turtles on it, and it shows.
Try rewatching it. It's unforgivable.

Jimmy stole from their father
Jimmy manipulated two girls and caused a scene at their mother's birthday AND forced their mother to drive them home
Jimmy tricked a woman into having sex with him by pretending he was Kevin Costner
Jimmy is not a decent man, and will only get worse in future

The rifle thing is a bit of a plot hole (but doesn't have to be), but that whole segment, the doc's office, the crossing, unquestionably takes place in Mexico.
And Brock would be waaaay too young. And it wasn't the same actors. And it adds nothing to anything.
But please, dismiss my counter like I'm the one grasping at…

You're right that Mike wouldn't cross the border with those drugs, which is why he acquired them through Gus' source in Mexico and used them while the Gelado truck was still in Mexico

No. It was 100% Mexico. The clinic was in Mexico. The stop where Mike planted the shoes was in Mexico (they stopped at an ALTO sign. That's Mexico). Your theory is wrong.