I think the watch is a 2-3 upgrade cycle.
I use to upgrade my watch every year until I got the series 5. I realised then that the huge depreciation in value and the incremental Juno’s meant it wasn’t worth it. I’ve preordered the Ultra but if I don’t get along with it or if I think it’s too big I’ll return it and get a series 8. Then I’ll see if they bring out a smaller Ultra next year.