I don't think anyone is trying to "deliberately" ruin anything. People in roulette generally want to run things quickly and efficiently, and those two story dungeons have some pretty hefty cutscenes.

When I first ran those two dungeons back in 2.0, I asked if I could view the cutscenes. The party was okay with me viewing said cutscenes so long as they could proceed forward with the boss fights. For me, that was a mutually agreeable arrangement. The bosses in those dungeons have always been easy, but at this point it is even more faceroll tier. You aren't missing anything profound by not fighting the bosses, so why not forego those fights in lieu of viewing the cutscenes? If you are really wanting to experience the bosses, however, you could always just enter the two dungeons again, this time skipping the cutscenes?

I'm not sure why OP and a few others appear to be still reeling over this sort of situation. Expecting that a group of people wait for you to finish your cutscenes so that you can also participate in the entirety of the dungeon just feels very...inconsiderate?