I am not a fulltime colorist, but so far I deal with this sensitivity. Until ACES I had to do the same with many log-formats. Now it’s just one
The conceptual problem with picking RRT/ODT values would be, that you would have to deal with a “working RRT/ODT” that is not the same as the “output RRT/ODT”. So for example if you would chose to work in 709 and therefore the colorpicker would select what you want (which for the real workingspace of ACEScct would be a different value internally) and then choose a different output (for eample outputting to P3) those values would not longer be the same unless you have that imaginary “working space just for the colorpicker RRT/ODT”. That’s so complicated that I am almost not understanding my own lines
So I strongly reccomend to getting used to colorpicking in log-space.
For the other issue of hitting certain colors:
We discussed that in at least 2 other threads, that you find here on the forum.
But in essence: The only way other then getting it close by eye is to get through an inverse of the RRT/ODT of whichever your output RRT/ODT is. As far as I know that’s pretty hard to do in Resolve. Maybe by the following workaround:
Make a sRGB TIFF with that color you need to pick. Without a coloprofile applied in Photoshop. Then import that into Resolve and apply a sRGB IDT to that. Now colorpick the value from what you see on the screen. That may be then perfect for a sRGB output and close for Rec709 output. But I am not sure what happens when you get to other ODTs. Probably it’s wrong then.