Nowhere did I say you shouldn’t have a staging environment. However, if you can develop and test changes locally then by the time it goes to staging, the code should already be in good shape most of the time. Staging is like your guardrail, it shouldn’t be part of your main dev loop.
Meanwhile, not sure what the issue is with running a monolith locally. The reality is that even large applications aren’t actually that big in absolute terms. Having to run a bunch of services locally to test things end to end is certainly not any easier either.