Possible that One Piece has desensitized me to things like this with all its fakeout deaths, but it didn't bother me at all here. I don't personally feel like it betrayed my expectations; I trust the show the to be interesting and fulfilling, so I usually make an effort to not set expectations with myself, or to even try to think about common tropes. If the show has earned my trust, I'm ready to be fully invested almost without reservation. I understand that's probably a me thing though.
But, in my opinion, it's paced like this because it increases the focus on Mob's distress. This series is about Mob, and at the end of the episode both Mob and the audience feel the same horror and tension. The focus is on what the character is feeling, because it always is. You have to linger on it and empathize with Mob. Changing the episode cut to what you proposed would increase the (I would say in some way less fulfilling) tension of whether or not they're dead at the expense of the emotional tension with Mob. Which of those someone prefers, and whether you bring external meta/literary/trope expectations into it, is obviously going to differ person to person.
Love your reactions <3