Mmmayday38 thanks for your comments and I'm glad that you understand my point is not to blame anyone but to understand the mechanisms that lead the sequence of actions, wrong or not. We all are subjects to these mechanisms and understanding how and why we do things is very important.
I found this very interesting point in your comment:
I chose to leave my First Officer handling the aircraft to allow me to attempt to diagnose and fix the problem.
This is definitely how tasks should be split, my next question is why the manual aircraft handling happened so late (or what processed contributed to delay the AP disconnection).
WojtekSz's analysis is very interesting, but it is not totally correct to compare flaps 25 and 30 with constant AoA. However, the interesting point is to see how much of drag is added by deviating from the best glide AoA.
Provided that his numbers are correct, we see that between 3 and 14 degrees of AoA the drag difference is around 4.37. Maintaining the best glide AoA would not only save 3 times more of drag than the simple flap retraction, but also produce more lift (thus significantly increase the gliding distance and Vz control).