nope, .xinitrx is only executed when X is startd with the startx command.
i dont know what scripts are run when init 5 starts X...
try as root
find | grep xinitrc (without the dot)
see if it finds any other xinitrc scripts (apart from the ones in your home directory, if it does, have a look inside, edit it to load kde or whatever with the same command as before, "startkde"