Having more than one schema owner is practically a death sentence for development and engineering...
We used to have a few of those, especially on exadata clusters. Finally carted them out of the local dc after moving to RDS Aurora databases with strict policies. Might have caused 3 or 4 people to quit, but totally worth it for the 500+ people that stayed who now can own their data, schema and development (and be held responsible for it! -- another issue of multi-db-access, it's always someone else's fault). Went from deploying once a day with a 'heads up' message to no-message deploying multiple times per hour.
Why monoliths? Everyone still wants to to have OLAP and OLTP systems where analytics are done on OLAP. Where having this separation you can get data from multiple sources to put into your analytics.
I cannot imagine people not doing that and having need to have stats in real time. For most shopping/banking stuff you can get away with once in 24 hours dumps and then analytics can be done on that.
Our databases are open to way too many people. What's worse, they are multi tenant making refactoring really hard.