what bike(s) is best for climbing (and then descending) road AND gravel? CruX? Open UP(PER)?
Depends what the descents look like. You want more “twitch” the tighter the corners are because some gravel bikes are designed to be stable and stay on a line, meaning if you need to carve a canyon like a TdF pro on a descent…that ain’t happening.
A cross bike in general will be the better jack of all trades for that IMO if and only if you put in the time to be able to handle the bike on loose surfaces.
I have a TCX and that thing can fit 650b with some bit tires these days, as a cross bike. And the handling is a LOT snappier than the 3T Exploro I rode. I can only assume a Crux or Boone or whatever cross bike to be similar to the TCX.