Derivative work and complete corresponding source has not been tested w.r.t. Google's monorepo (or similar situations), because under the terms of the gplv2/3, Google doesn't distribute any software.

There's an entire class of tooling to make sure that GPL-tainted software isn't distributed (https://opensource.google/docs/thirdparty/licenses/#restrict...), but because the class of software that Google distributes under the GPL is limited (can you think of any?), this is workable, and such things can be isolated.

That doesn't work if the definition of "distribution" is broadened significantly. Then the derivative work questions (which aren't as cut and dry as you claim) do suddenly matter a lot more.