The gap of features missing is documented here: https://www.pingcap.com/docs/sql/mysql-compatibility/
I would rate compatibility as actually pretty good: all but one SQL mode is supported (which is a feat in itself), and most of the SQL functions are supported.
There are some exceptions though, some which are addressable (missing functions) and some that are not (often a property of being an optimistic system).
We try to be as transparent as possible on this, which might be part of the reason why you feel there is a lot missing?
If you have specific examples, I would be happy to clarify. We also have a course designed for MySQL DBAs, which is designed to make the adoption easier: https://www.pingcap.com/tidb-academy