Assertion 1:
- Pro: The build environment is guaranteed to be what's expected
- Cons: It slow down validation of patches.
Assertion 2: Exactly the opposites pro and cons.
I'd advocate to let developers have docker on their system to iterate quickly on fixes or advancement and keeping regression and integration tests in the CI pipeline. That's not required, every dev should be able to choose if they just code and never run anything locally or if they want to run whole test suite on their workstation.
So both assertions are valid, I see no valid reasons to enforce one or the other