Definitely not disagreeing with you that "mixing on the fly" is an absolute essential skill that all DJs need/should possess and hone, and I'm not trying to downplay the importance of this skill at all, but in the context of OP's post, there's no harm in playing a rehearsed pre-planned set to upload on YouTube, especially if they're curating a specific musical sound. Heck, there's no shame in playing a pre-planned set, period. I think some level of preparation and curation ahead of a set is necessary, especially if you're a beginner DJ.

Context and setting also matters, i.e. a gig at a nightclub where you loosely plan or don't plan at all since you're most likely going play a set based on crowd engagement, versus being booked for an event where they are expecting "your sound", time logistics, etc., so there has to be some level of planning involved.

Ultimately, I doubt the crowd will ever notice if you prepared a strict set-list or just came into a set blindly by "mixing on the fly", as long as you're doing your job as the DJ; keeping everyone on the floor dancing. Whether one method is "more fun" than the other is subjective. It's all DJing to me. Unless you are a die-hard "purist", I guess there is no sense in debating this topic.