DL's RM software has better predictive capabilities than you do. DL believes that it will sell those seats for more than the competitor is charging, so it has no incentive to sell them on the cheap. Perhaps the competitor's customer profile is different. Perhaps the competitor got it wrong and will lose its shirt. Perhaps DL got it wrong and will lose its shirt.

The seat map is also a useless tool. Chrismas to the Phillipines could be booked solid with consolidator tickets who have blocked space, but have no seat assignment. The aircraft could be close to sold out for all the seat map would tell.

But, the real bottom line is the it makes no sense to complain to DL. You only confirm DL's view that sooner or later, you will pay. Better than complaining, just go book the better deal. Why on earth would you pay more than you have to unless there is some value proposition to pay more? And if there is a value proposition, I guess that DL gets to charge more.