I think the yearly updates schedule is part of that too. It lends itself more to gradual improvements and change. It’s not going to be a huge new feature set like ZModeler every single year. But I’m not sure I see any real sign that ZBrush development is resting on it’s laurels. Nor slowing or loosing focus. The updates recently all have big improvements and are actual real updates. And everything they add is always brilliantly thought through and stable and usable from the get go.
A lot of the dizzying activity and fast development happening around Blender right now is surely that a lot of feature and add-an development had stalled because everyone was waiting for 2.8 to be ready ? Now it’s finally out and getting established and stabilized it feels bit like like a massive development dam is bursting.