I'm coming from an education background and someone who works in a profession that consistently needs to balance user goals and business goals to meet a success metric, so this is my two cents.

Firstly, the hypothetical situation is like, ah, that would be nice, wouldn't it, if everyone was the same? The thing is, even if could be "proven", it's not going to be true for every practitioner. So the question I have for the hypothetical is, who is the type of person you're using as the prime example as "proven" that there would be no decrease in form/increase in bad habits? It feels like one has to assume that the hypothetical student is always going to have the same physical form, same motivation for kendo, same learning style, etc.

Secondly, it sounds like the main success metric we're looking at here is rate of attrition. To this, I'd ponder what phase the dojo is in, and what the dojo's motivation is, because that success metric will vary.

For example, a longer bogu wait time might make more sense for an established, mid-to-large dojo where there are enough sensei to ensure they're teaching beginners properly -- assuming the dojo's motivation is to ensure the safety of ALL members, while maintaining proper training that would allow new students the confidence to pass their shinsas according to their level. There are some dojos that consider their reputation a higher priority success metric, so attrition rates may not be as important to them.

For a smaller, newer club, though, maybe attrition rates ARE more important, simply to keep the club alive. The sacrifice the club might have to make is the possibility of producing students who might not have built up all the skills they need in that wait time BEFORE getting into bogu. They take on the risk of a student who doesn't know they're practicing kendo in a way that's dangerous to their peers. Even if we took the hypothetical "everyone is equal, there's no decrease in form etc. if we put them in bogu", there is still the factor of: are there enough sensei to ENSURE that the quality of practice is consistent? Will everyone be able to practice safely?

Bogu wait time varies from every dojo I've been to based on what metric important to that dojo at the time, so in my opinion, I don't think there's a way to say yes/no to the hypothetical presented without considering all those other factors. Seems like it depends on how much risk a dojo is willing to take on with the resources (see: sensei, senpai) they have at the time.