I found this in the documentation, section '5.11.3. Partitioning Using Inheritance'[1]: "Some operations require a stronger lock when using declarative partitioning than when using table inheritance. For example, removing a partition from a partitioned table requires taking an ACCESS EXCLUSIVE lock on the parent table, whereas a SHARE UPDATE EXCLUSIVE lock is enough in the case of regular inheritance."
This point is no longer valid with some restrictions. If the table has a default partition, then removing a partition still requires taking an ACCESS EXCLUSIVE lock.
May be make sense to add some details about DETACH CONCURRENTLY to the section '5.11.2.2. Partition Maintenance' and completely remove this point?