Hey Mike,
Thanks for the quick reply!
I already tried to pass a mapped class to Insert() but it didn't work (because the mapper is joined-inheritance and so it needs to insert a row in both the Base parent table and the child table). Got an error about "Unconsumed column names", because the values contains (through inheritance) fields from both table.
I ended up doing a "mass" query check to separate bulk_insert_mappings and bulk_update_mappings :
https://pastebin.com/raw/JTpSsMEwNot the best performance deal compared to on_conflict() I guess but that's all I found for now.