impdp with TABLE_EXISTS_ACTION=TRUNCATE uses external tables but shouldn't

I'm replicating a table via Data Pump and impdp does a direct-path load with TABLE_EXISTS_ACTION=REPLACE (~5 minutes) but falls back to external tables with TRUNCATE (~30 minutes), regardless of whether it has indexes or partitions.

• The source table has partitions and two indexes, one of them unique
• The pre-existing destination table, in a minimal test case, has no partitions or indexes (let alone unique ones):

CREATE TABLE lc_account_tbl (
  lc_account_id        NUMBER                      NOT NULL,
  record_state_ind     NUMBER(2,0)                 NOT NULL,
  subpartition_key     DATE                        AS (TRUNC("LC_DATE_TO")) NULL,
  account_fk           NUMBER                      NOT NULL,
  lc_state             VARCHAR2(3 CHAR)            NOT NULL,