Sale was his "boy." The others were here before DD.
IMO, DD wanted Betts, but he set a price that all agreed on, and when they knew he wouldn't take it, the plan was to trade him, even before Bloom took over.
I don't see how this led to DD's firing.
If JH wanted Betts signed over Sale, he would not have allowed the Sale signing.
If JH wanted to offer more, but JH said no, why would that be grounds for firing, unless DD called JH a dick or something.