As per my earlier comment, ~/.zprofile and ~/.bashrc have to source ~/.profile, but that's always been true.
Quotation needed for the "that's always been true" part. When you run zsh and it creates the default .zshrc, it doesn't source .profile and I doubt zsh users do that commonly.
Regardless, neither of these files is used for the non-interactive non-login shell we are talking about - the paths must be set in .zshenv in this case - check the diagram.
Finally, you can't source .profile in shells which are not bash compatible like csh, tcsh or fish.