Olga K.
Re your questions "What I'm trying to understand is: are there specific use cases where the native HubSpot integration becomes genuinely essential and can't be replicated with a CSV import? And is that worth the upgrade on its own?"
The answer is yes but potentially not for your current stage though it depends exactly what use cases you currently use Clay for. But for instance if you want it to run as the base for your hubspot data model so that no matter which source your data comes from it's always (no matter what), cleaned, enriched, validated, uniformed and follows your internal taxonomy so that:
your reporting is cleaner at company wide level
you marketing campaigns are easier to setup
your overall CRM data stay clean and up to date
The the integration makes sense.
This is only one rev ops use case but there could be many other to automate your overall revenue engine for which that would make sense to use it. For sure as you scale it will become necessary,