I've found that adding to xsessionrc
is what made it work for me, I actually tried to source the
GUIX_PROFILE/etc/profile, but I could not make that work reliably
(seemingly .xsessionrc dost not cut the bill here)
Did you just create the file adding the export PATH line that is also in .profile and that's it in the user's home folder? I've never had to deal with .xsessionrc before, I am reading different sites on the web, but maybe I am doing something not in the right way.
Just in case something went wrong in between, I am following your steps, and documenting it.