If someone felt they had a genuine need for an important meeting with an unknown scope, unknown attendee list ("all hands" suggests that they don't know the nature of the issue or whose expertise will be needed in resolving it), unknown objective, and it sits outside of the normal incident management then I would still ask them what on earth the meeting was about. After the fifth time someone asked, and they had to take time explaining it, they might start regretting not giving any kind of context in the meeting invite.

> If you don't make time for back channel sync, you will become an isolated island and your product will eventually suffer.

This doesn't seem to align with your hypothetical example. Of course, for project sync, there should be regular sync meetings, and cross value stream meetings. There should also be design reviews and retrospectives (both regular and ad hoc). It would not be appropriate to schedule any of these without an agenda or scope.