DBMS_RESOURCE_MANAGER limit IOPS or MBPS
By making those processes slower you als stretch the period with pain for both the regular users as well as the etl processes. We normally solve this by assigning a dedicated replica to the etl/reporting processes. That replicate can be tuned to better support the etl processing and it removes the need to put the extra pressure on the production database.
Resource manager can be used to prevent long running queries from starting at all. Problem here is that the estimates it uses are not always correct which might cause regular queries to be rejected. So be careful.