It's still serializing the data when it send it over the database link:
https://asktom.oracle.com/pls/asktom/f?p=100:11:::::p11_question_id:3561967900346593583 You could still try reducing the number of parallel process, running it serially or trying DIY parallelism.
Alternatively, if this is one-off operation you could export/import the data, use transportable tablespaces or some other offline approach.