First and foremost, I recommend using the "undersized" option in Duty Finder and doing these dungeons with as few as two others that are happy to wait for you to properly watch cut scenes.

Secondly, common though it may be, players trying to force you into speed running it has never been an acceptable thing. If they refuse to play nice, it's actually something GMs will punish if you take the time to report it.

Thirdly, "instance" doesn't mean what you think it means. Every dungeon is an instance. They're "instanced" in such a way that it's private to the group of four or eight. Instancing does not necessarily mean it's solo. It sounds like you're saying you want this to be solo content.

Personally, I think the fix would really be to just put all the lengthy cutscenes either prior to actually entering the duty or after completion of the duty.