If Gandalf STFU they could have stealthily walked out of Moria but Gandalf wouldn’t have all that sick XP to himself and level up to The White Wizard prestige class.

Ol Ganny was power gaming. He even got the rest of the party to retreat so he wouldn’t have to share XP points.

Hmmm, the same might be possible in the book too:

Pippin felt curiously attracted by the well. While the others were unrolling blankets and making beds against the walls of the chamber, as far as possible from the hole in the floor, he crept to the edge and peered over. A chill air seems to strike his face, rising from the invisible depths. Moved by a sudden impulse he groped for a loose stone, and let it drop. He felt his heart beat many times before there was any signs. Then far below, as if the stone had fallen into deep water in some cavernous place, the came a plunk, very distant, but magnified and repeated in the hollow shaft.

‘What’s that?’ cried Gandalf. He was relieved when Pippin confessed what he had done; but he was angry, and Pippin could see his eye glinting. ‘Fool of a Took!’ he growled. ‘This is a serious journey, not a hobbit walking-party. Throw yourself in next time, and then you will be no further nuisance. Now be quiet!’

Nothing more was heard for several minutes; but then there came out of the depths faint knocks: tap-tom, tap-tom. …