I disagree, and so does the company, in a roundabout way. Domestic reserve stretches are limited by Delta to 6 days max to comply with the FAR 24/7 rule. So, on the front end they acknowledge those are, in fact, duty days even if you are not used. Then, on the back end, they say "Oh, wait. That was really free time because we didn't use you." The company is playing on both sides of the net and has apparently been doing so for a long time.

The fix is actually quite simple: just insure the pilot has 9 hours free of duty prior to the start of the next SC.

The real problem for the company is the long-call-becomes-short-call practice. Any transition to SC would require 9 hours notice, a solution I personally am in favor of.