Not too familiar with RISC in general, but wouldn't a Cortex X1 be the same uArch regardless of implementation? I suppose the A76 and A78 could be different, but over half of the chip is identical cores.
Nope. ARMv7, ARMv8 (and friends) are called
architectures.
Microarchitecture is the technical solution (the silicon) that implements an architecture.
Cortex X1 would be the same, but Cortex X1 is one of the microarchitectures implementing ARMv8 architecture. See:
https://en.wikipedia.org/wiki/ARM_Cortex-X1
This is pretty muddy, because while ARM designs architectures, they also design reference implementations, such as the X1.
That said, I now have to correct my previous post. Up until recently, Exynos meant Samsung's own implementation of A7x or A5x cores. They've supposedly stopped doing that, I'm not sure whether their current cores are customized anymore or they are plain ARM reference designs. In the latter case, Google's Tensor would not be an Exynos. I need to do some Anandtech digging, but I don't have a lot of time on my hands.