There’s quite a few rigid steel bikes been through my garage in the never ending search for biking heaven, there’s three I’ve kept hold of that will be with me until I die. They are:
A Niner Sir 9. Bought as a secondhand frameset from Ebay, it’s running singlespeed. I can’t pin down what I like about it other than it’s really nice to ride. I’ve owned the usual suspects, Charge, Cotic, Genesis etc, none are a patch on the Niner.
Jones. I bought this specifically for the Divide but it’s so good at just about everything I’ll never get rid of it. If I only had one bike this would be it. It’s the original 29er before the LWB/SWB stuff came out. The do occasionally come onto the secondhand market, it’s always worth asking on the Facebook group. The new SWB fit’s the OP’s brief perfectly, it’ll take B+/29er wheels and has bosses galore.
Lastly I’ve got a Jones Spaceframe. It’s as capable as the diamond and rides exactly the same, mine as a 3.0 front tyre, just because. It gets a lot of comments when it’s parked up, wifey seems to have first dibs on it as her bikepacking ride. The frame bag is smaller but we never carry that much stuff anyway.