My threshold for a rebuild is certainly lower than yours, but definitely higher than Harry's. Anyone who watches baseball will see teams, every year, that will be approaching the end of a contention window, be terrible, or be sitting in the dreaded 75-80 win limbo. I think its pretty easy to identify each team in a situation like that and, usually, I think a rebuild is the best course of action long term. Sometimes I'm wrong. A year ago I thought the Angels were in the absolute worst position in baseball, with a team that couldn't contend and their most valuable trade chip being virtually untradeable because of how cost prohibitive he is. They also had the worst farm in baseball by far and huge albatross contracts limiting their payroll. Fast forward about 18 months and they got super lucky with Shohei Ohtani and managed to build at least a semi-respectable farm. They haven't proven that they can really contend yet, but I like their long term outlook enough where I don't think they need to rebuild anymore.
But most of the time, if a team isn't in a contention window, I think the prudent move is to commit fully to a rebuild rather than trying to compete against really long odds. A lot of the time those teams that are close to contending, but not quite there, have enough valuable assets where they can do a quicker rebuild than teams who allow their contention window to end because they let all of their assets walk. The Royals are gonna be in really rough shape for a long time because they let that happen. They thought they were competing in 2016 when they really weren't and its screwed up that organization for years.
And I get how rebuilds suck for the casual fan, but for me I actually really enjoyed our rebuild. It sucked losing, but watching our farm system grow into one of the best I've ever seen and dreaming on some of our top prospects was pretty enjoyable for me. I think we can have a long-sustained contention window, but if we ever get to the point where it looks like it is coming to an end, I'll be advocating a rebuild like I would for any other team.