Even if we assume serious and dedicated security ops at these organizations, the attacker can specify the port to connect to. So any firewall would need to deep

Even if we assume serious and dedicated security ops at these organizations, the attacker can specify the port to connect to. So any firewall would need to deeply inspect outbound traffic. And plenty of ETL jobs can mix in offsite data e.g. pulling from S3, or even from a hosted LDAP solution, so they wouldn’t prevent outbound traffic. The attacker could even use AWS IPs! As I said, a perfect storm.