Ditching an architecture also directly implies adopting a new one. If juniors are at the forefront of that, I don’t think the resulting architecture will somehow get magically simpler.

Architecture is a topic to be debated, no doubt. But if anything, I’d expect the departure of senior talent to solidify complexity, not enable some magical escape from it. The risk of changing a system goes up significantly the moment the people who understand the system walk out the door.