The bottom line first: Drop it. There is nothing to push. You have DL's decision. When Marsha told you, after four rounds that it is all over, it means that DL will back her up unless there is some horrible misunderstanding. There is not.

A better way to put this is: What do you want from DL above and beyond an apology?

DL basically owes OP an apology and a dinner (it was a MX delay which led to the misconnect). You got the apology. I would forget about the dinner. But, the problems here are the nature of creeping delays which are usually unavoidable.

As soon as OP misconnected, he had missed the only flight which would get him to downtown Tel Aviv for a meeting the next afternoon.

The only other option out there which would have got you to TLV any earlier than the later DL service, and it still would have eaten up the bulk of the afternoon, was the LY service at 7:00 PM. You have not advised whether LY had availability. Perhaps it was full?

Given that DL has a later service with space, it is fairly reasonable to refuse to rebook you onto LY.

I have no idea of the fare you paid or what LY was selling for that night. But, for a random day next week, it would cost an extra $30 to fly LY over DL. DL did offer, as it is required to, to refund its ticket. So you could simply have headed over to LY and purchased a ticket.

As to C+, I presume that there were no seats. DL, of course sells those and you offered to pay.

I get that this was a bad experience, but the only aspects which could have been handled better had to do with customer handling. The broken aircraft took the time it took to get itself fixed and so forth.

As davetravels notes, if the purpose of this trip was time-sensitive, you pushed the envelope too far here. This trip required arrival a day earlier just because planes break, weather intervenes, and things happen as they did here.