Of course true modules would work even better. The only reason I suggested the manifest entry is because I thought it might be easier than converting to modules wholesale.
That's true indeed. automatic module entries were added mostly for EE 9. For EE 10 the ID was formalized and each API should have a module-info.java (be a true module). Every place this is missing, such as it seems in Faces, is really a bug and should be addressed as such.