Modern architectures look like this: https://github.com/donnemartin/system-design-primer
It is generally not feasible to recreate all of the elements of this design in a totally separate testing environment.
We have 2 GCP accounts. One for production and one for test. Same Setup, not an issue due to terraform and the cost is reasonable for a test env.
(Rhetorical questions. Of course the answer is no.)
All of these things have huge impact on the actual similarity of the systems, and consequently how they behave.
If it wouldn't make sense for us to have test and prod, we wouldn't do it but i can't imagine a scenario where this is NOT beneficial.