1500 hours in part121 is fine,but no number certifies minimum quals. The entry level standards should be subject to strict controls of the line itself. This Captain, all respects, failed a number of checks. Allowing to enter, and continue to fly, while demonstrably unable to perform to industry standards is unacceptable, however commonplace the practice may be.
Add to that impossible situation the difficulties with deadheading, no standard of rest (observed) etc. and we have what we have.