With managed tables on DBFS root and a few other cases, the UC migration is not straightforward.

do you mainly have managed tables on DBFS root? if yes, I agree with the time and complexity concern and don't really have an easy answer there except to recreate the table with data in the UC catalog.

But if you use external tables, it gets quite simple, and also, you don't really have to set up two environments as you can try it out first in your dev/QA and do in-place updates to code in production gradually over time.

Generally, I have seen customers have a mix of managed and external tables, but the %age of external tables is high...so only a small subset of assets and related notebooks, jobs etc, have high complexity.

Also, it will be worth checking in with your databricks account executive on different options to help speed up migration through different avenues such as delivery solution architects, professional services, and partner services.