Delta did indeed operate SEAHND the minimum allowed by the rules to keep the slot.
Like it or not, they were following the rules.
When AA objected, DOT issued new guidance, which Delta followed, operating the route daily.
Eventually they decided to return the authority to the DOT, which gave it to AA.
Let's not act like Delta defied the DOT. They did what they could within the rules, but they never broke the rules.
Did DL technically satisfy the rule? Barely. Were they utilizing the frequency as advertised during the route award process? No. Has DL been by far the noisiest player in this process and yet made the poorest use of their frequencies? Yes. DOT was right to change the terms of their award.
If you got back to the award process DOT always talked about maximizing these authorities for the flying public. Again something DL has undermined at every stage. Their strategy is to say anything to win then when they control the authority to bend it to their needs without letting other carriers compete again for the authority.
No arguments there. Delta played around with the process, but they didn't break any rules. We can go back and forth as to WHY they did what they did, but frankly, they were trying to make poor times work. No other airline made any request for the route authority until AA did, so I honestly don't see what harm came from it, as once AA objected, Delta obeyed the updated guidance from DOT until ceding the authority.
We could debate whether SEA-HND, even seasonally, is better or worse for the flying public than adding AA on the crowded LAX-HND route years ago. It probably isn't, but it's a reasonable debate to have.
Since daytime slots have become available, Delta has not deviated from their proposal. MSP and LAX were proposed on the 777, and that's what they have flown as (okay, to be fair, LAX is on the A330-300, but that was an increase of 2 seats).
For what it's worth, I don't fully agree wtih Delta's flexibility request here. I can see the argument that if the Japanese carriers have flexibility, the US carriers should too.
But if, for example, the DOT award Delta 2 authorities for ATL and SEA, for serving Southeast/Northwest regions, I don't think it'd be fair for Delta to then be able to move then to say, Detroit and JFK, as it undermines the reason they got the routes in the first place.