Hey, I think you should have just posted this in the ADV beginners, the ask any question thread for showdown, or in ADV OU discussion. In addition, you need to ask for permission to post here before just posting threads like this, so I'll be locking and moving this.
To answer your question, when showdown was implementing ADV, there was a long discussion about whether to follow the "port priority" of cart mechanics or do the speed based switch mechanics of later generations. I know PO used to randomly assign priority, I came up there, however (my opinion) I think it gives a more competitive experience to get that information for speed rather than just be randomly assigned. The OU council has agreed with this and that's why it is the way it is. I think the poster you cited in this video hasn't been around smogon in quite some time, because these issues were decided at least 5-6 years ago and this video was posted yesterday.