Interesting. But still not perfect. His explanation on the subject is a bit confusing but fair to say he does mention his knowledge doesn't reach that far into color science.
I think Fusion operates "as intended" by the design team but comes with a flaw for motion design. The problem here is that Blackmagic created an expected workflow for color managed to automate the process instead of giving the artist control over it.
If I'm not mistaken, what's really happening under the hood is this:
Whenever you work in DaVinci Color managed, the Fusion page automatically becomes a "managed" linear version of the working timeline color space. So for DaVinci Wide Gamut/Intermediate it becomes DaVinci Wide Gamut/Linear. The Fusion clip in your timeline is automatically converted from DaVinci Wide Gamut/Linear back to the working space DWG/Intermediate and then the output space follows.
In a way this makes sense for compositing tasks on camera footage but Fusion itself was never designed to operate with a working space to begin with making it more similar to After Effects than Nuke. In Standalone it's up to the user to work in whatever color space, gamma and bit depth via the use of nodes.
In ReFusion with color managed however, any MediaIn inside Fusion is automatically converted to the hidden working space which is also why the input gamut and gamma settings on that node don't do anything. It takes the Input Color Space from the Media Pool. This works fine for your footage because it creates a perfect roundtrip.
Where this idea breaks is when you want to deal with display referred color data generated inside Fusion itself. The range between 0-1 linear ( generated by your 8-bit style text color picker) is still living in the DWG/Linear values. Managed converts a value of 1.0 back to the log Intermediate and applies tone mapping. The resulting value doesn't come any close to display white and neither will any other color match.
For reproducing the chosen color you'd need to inverse the hidden color pipeline before it happens to cancel out it's operation so what goes in comes out. That's why you go from chosen display output back to DWG/Linear in this workaround.
I say it's not perfect is because while you do get an exact color match, I think the font aliasing/alpha data gets messed up no matter what because the alpha channel gets taken along in the conversion while it should be considered as 'raw data'. The other problem is your display output. You pick colors usually based on client brand books and those are pretty much always defined in 8-bit sRGB. If you need those colors but have a different deliverable format you still end up with the wrong colors.
I haven't thoroughly thought of an elegant solution for this ReFusion mess but I hope the design team can come up with something robust that also makes sense to the user. We at least need to get rid of the assumed workflow and either fully integrate DaVinci Managed into ReFusion's ecosystem with full control or totally separate it from it but give the user the option to define whatever the clip data is including an option to totally bypass management.