Pulling dungeon boss while newbie in cutscene

Several times this week I’ve queued to enter a dungeon to go at normal high speed through it with a newbie. They’re able to keep up with the tank, no problem so far. However, on reaching the dungeon boss and the normal cutscene plays, the tank pulls the boss immediately while the new healer is watching. When I pointed this out, the tank indicated “I won’t die while they’re watching, they can join when they’re done.”

While it’s objectively true, I do feel like it’s just good etiquette to wait for cutscenes before jumping in so all players are ready. If you are tanking, do you pull regardless of cutscenes, or wait? Does the dungeon or type of content matter (ex: normal dungeon vs alliance raid)? And am I out of line for asking for a moment on someone else’s behalf as to not have them feel rushed through a short cutscene?