In the old system, where cutscenes are skippable, players could have politely waited on the occasions when one player was watching the cutscenes. With lots of people running the roulette, the chances of your party getting that new person should be relatively low. There would be a gamble of your time when you queue for it - will you get a party that can speed through, or not? - but first-timers get their climactic finale and everyone else gets their 15-minute run most days.
Instead, people refused to wait - and so the developers have had to "take a side", decided the new player's experience is more important and the (only?) way to ensure that, at least without heavily revisiting the content, is to make the others wait. And if the game framework doesn't allow for dynamic "sometimes forced, sometimes not" cutscenes then the only way to achieve that is to make everyone wait, every time.
Ideally there could have been some kind of warning before it happened - "if you don't voluntarily wait for new players, we will have to force everyone to watch cutscenes every time" - and maybe people would have listened to that and realised it would be better to wait sometimes than to lose the "quick run" entirely.
(I'm guessing the game's coding means they are not able to implement a dynamic "unskippable cutscenes only with a new player present" setup, or they would have done so - but in any case it comes back to the ideal scenario of the old system. If people chose to wait for new players when necessary, that would have the same final outcome, without needing to force it at a programming level.)
Saying that "changing it the way they did was just a dumb idea" can come across that way, because the change was specifically meant to help first-timers. Thus, an interpretation that 'changing it for the sake of first timers was a dumb idea'.