I understand why cutscenes are unskippably played (and very slowly played when it comes to text prompts) at the moment: It's so that newer players can watch the story scenes without having to worry about gameplay interruptions. I'm also aware that this is the main reason that high experience point amounts are granted, so that higher-leveled players feel an incentive to join the roulette to ensure that newer players can get their needed clears to advance through the game's story content.

...That all said, if an instance is started and the game detects that there aren't any new players, meaning that there's no poetics bonus message, what value is there in the roulette still playing the slow text scenes if everybody has already completed the instance? It's a punishment for the sake of a reward, but it adds no value to the game, only harm.

Personally, I would like to see those two outdated dungeons completely replaced with lengthy single-player instances, but if that can't be done for... whatever reason, then doesn't it make sense for the instances to either require at least one new player or not play scenes when there are no such new players?

Yes, the latter means that there could be instances where nobody is new to the dungeon yet may still receive high rewards, but again, this could also be solved by forcing there to be at least one new player before one of the dungeon instances can be kicked off. My problem is that you can run into situations where the players are being exposed to lengthy periods of waiting but for no perceived benefit to any newer players due to newer players being absent, and that seems unhealthy to me. The systems in the game encourage this as an easy way to gain lots of experience, and thus many players will follow a broken system even if there's no benefit for any newer players.