My position at this point in my Jiu-Jitsu journey is that more value is gained from positional sparring period (and as I said in the other thread, that includes things like starting separated from the feet or in a specific Clinch situation; it’s not relegated to ground positions or an excuse to avoid developing takedown skills/defense). Other than allowing students to test their transitional skills (demonstrate their ability to progress from a neutral position to a dominant one to a Submission) or just have fun (which to be honest does have some importance), I honestly don’t currently see any reason to place a substantial amount of time or energy into free rolling.
Drilling takedowns from the knees can still be used to teach people about things like Connection/Disconnection, Kazushi/off balancing, base, and even some takedowns that are directly applicable from a standing position (such as a Snap Down, Knee Tap, Arm Drag, and Sag Headlock to name a few). So, while it’s not as specific to actual Grappling or Combat situations as starting from the feet I would not really advise “always” pulling Guard (though that is a viable option as well). And, if someone had to “fight really hard” for a takedown (which I take to mean using a lot of effort/athleticism), then they aren’t very good at that takedown/from that position which actually means that they should spend more time in that position (and of course refine their knowledge and understanding of their techniques) so they don’t have to expend so much energy. Now, again, whether that is worthwhile (based on how often they actually wind up there) is the question.
Another thing to understand, IME, is that people don’t really question or examine their training practices like they should. There is a lot of “this is how I was taught/how my instructors did it, so this must be the way I should do it” type of thinking in the Martial Arts (and athletics, and life for that matter, in general). In many cases though, how someone did things in the past not only might lack the context for “why” they did it that way, but also may have very little validity as an argument for why someone should continue to do things that way going forwards. There are no shortage of practices from years past which the practioners of would have likely sworn on their effectiveness, yet have long since been discarded in favor of more objectively valid methodologies.
So there is a good possibility that this guest instructor is just repeating what they were taught without any real investigation or reflection on whether having people start from their knees/free roll regularly is really the most effective way to teach their students how to effectively grapple.
Just some more food for thought.