As I've marked here, both default expressions are depending on the sequence, but there's only one "ownership" dependency of the sequence on a column. To complete the switchover you'd need to use ALTER SEQUENCE ... OWNED BY ... to move that ownership dependency to the new table. Then the old table (and its default) could be dropped without affecting the new table.
I did an alter sequence after the table renaming and it works now. Thanks for all your help.