1: Germany has strict laws about "slap a badge and call it a day", mainly, you aren't allowed to do that.

The fuck are you taking about, no they do not. All manufacturers do this:

https://en.m.wikipedia.org/wiki/List_of_badge-engineered_vehicles

A good percentage of the car has to be unique. That's why the Z4 and the Supra have different bodies and suspension - which going from a convertible to a hard top drastically changes how a car behaves.

Cool, no one said they weren't setup different. It's still a z4 hardtop which BMW built. That's why the Toyota techs had to be trained with BMW and they order parts from bmw...

2: Car mags nothing, the Toyota lead engineer that worked on the project, as well as video documentation, says otherwise.

It's called marketing, they didn't magically do shit to that motor, it's still a B series.

3: You didn't get a Mk.5 anyway, so do you know the difference?

Yea, it's still a BMW. I don't know why you're so upset about this.

Or did you roll in a Z4 and assume it's the same? Can you tell me how they "felt the same"? Is it just the BMW active diff wiggle under power? Or are there other tells?

How it drives vs what and who designed it are two different things. You're basically trying to say "if your point held any truth, then all BMWs would handle the same". That's not what anyone is saying. It's built by BMW, using BMW parts, from a car they already had. It's a hardtop z4, with a Toyota badge and nothing will change this.