Yup, the D will feel “slow” for sure, even if you had identical tires and wheel between the bikes. Some may not like that, but the purpose is to make it more stable and predictable in “bad” conditions.
The discussion in the podcast is worth a parallel consideration:
It focuses on MTB, but the concept of getting a bike that is SUPER capable in tougher conditions (Diverge better than the OPEN) can give a rider more confidence to learn and improve. That is compared to “under-biking” with the OPEN and riding something that takes more skill to do the “same ride”. So the Diverge geometry is the “aid” in this instance (like the geo/tires in the MTB), with an aim to making difficult terrain easier and less scary.
Both can be ripped to a similar result, but what they demand from the rider, and the experience in doing so will vary.