Sorry, but nothing in your complaint has anything to do with DL other than perhaps the delayed luggage and there is no way to comment on whether the 20% if fair without knowing 20% of what.

First, your delays at US entry formalities at ATL (CBP) have nothing to do with DL. If you were traveling on a Diplomatic or Official passport, you should have had access to a designated lane. If you were not traveling on such a passport, but simply to an official function, you are stuck standing in line with everybody else. Either way, your complaint is with the US government and not with DL.

Second, DL requires that you be at the departure gate for an international flight no later than 30 minutes prior to scheduled departure. You were not. At that point your seat was given to a standby passenger. DL has no way of knowing where you are. Perhaps you did stop for a meal, a drink or whatever.

Third, It's hard to comment on the 20% issue without knowing exactly what you purchased and submitted. Generally, DL will reimburse necessities and reasonable expenses under the presumption that you would have the first few days clothing in your carry-on. The same would be for the unfortunate situation in your hotel room. But, let me stress "reasonable". I don't know what you spent, so please provide the specifics: what did you purchase and how much did you spend?

Last, the missed meetings and the like are all consequential. Even if not, the delay was caused by CBP, not DL.

Bottom line here is that you are blaming DL for something that has nothing to do with DL. You made a smart move by allowing an extra day before important meetings. I would suggest leaving a greater connection time and also packing key items in carry-on. This means not having to rely on others.