[shoo]

Reasonable engineering decisions depend on context.

POC-quality code that doesn't have clean boundaries and is tightly coupled isn't necessarily a problem if it is an internal detail of some application or library that is cheap to change in future if necessary, and its impact is localized. As long as it works, if there aren't any forces that cause it to be revisited, maybe it can be left to be low-quality forever, without any further impact.

Where things get concerning are if the cost and coordination required to change the design in future grows over time or becomes effectively impossible. E.g. if the POC-quality stuff ends up being propagated internally throughout the codebase over time as developers make changes and add it into more and more places -- maybe its within the control of a single team to fix it, but if left unchecked the effort grows from a few hours work in once place to something requiring planning, systemic refactoring, testing, dedicated effort over a period of months.

Or, worse, if the POC-quality poor design has ended up polluting system interfaces between components owned by multiple teams or multiple organizations, so removing it would become a multi-month or multi-year coordination process between groups of people with different priorities, requiring a V2 release, deprecation of V1 & migration.