It actually kind of feels to me like a CPU that only accepts x86 machine code. You've got a complex system with firmware that implements a portable API by generating programs for a non-portable custom microarchitecture.
It's not like we haven't seen CPU microcode bugs, and it's not like the CPU doesn't have access to the whole system. The real issue I see with the raspberry pi drivers is that the GPU is a bit like the 386, where the OS can't effectively constrain what the firmware is willing to do for userspace applications.
And there's the different history: it's like if we'd historically never had an x86 chip, and had been emulating it on the Z80 using a secret proprietary optimizing emulator. And then someone comes out with a microcoded x86 chip, and this release is obviously not informative at all about anything that we didn't know before.