People should absolutely be planning their work. Measure twice, cut once. But then again, isn't agile supposed to be iterative? Measure, cut, measure, cut, measure, cut.. repeat?

How much value do you get from putting 20 engineers in a conference room for 2 hours, 2-3 times per week? What if this is mostly just a head strong manager who enjoy monologuing his captive audience team?

Note I said "spent 30% of our time talking at high level management view about doing work rather than just technically planning & doing it" This doesn't really help prevent building things that don't fit together at all. It barely allows you to surface technical dependencies and order of operations.