I've had the same experience, cross-department shadowing at a listed fintech. It worked tremendously well... For 3 months until they invoked "too many meetings" rule to shut it all down. IMO it died because it exposed how many people's entire job was controlling information flow. The "useless humans" you mentioned? Their job security depends on being the bottleneck. If developers understand customer problems directly, what's the PM doing all day? If sales knows what engineering can actually deliver, why do we need three layers of "roadmap prioritization"?

When engineers can talk directly to customers, when support understands the product, when sales knows what's actually possible, suddenly half the middle management layer has nothing to do.