There are no "gear indicators" on there because what gear you are in is quite meaningless, as you correctly noticed ("based on perceived effort"). Aside from a

There are no "gear indicators" on there because what gear you are in is quite meaningless, as you correctly noticed ("based on perceived effort"). Aside from a little dance on the chainrings you shift up and down merely to keep cadence in check. And yeah, we might all be guilty of starting to turn over too big a gear as the mind wanders, but surely not to the extent that somebody needs to tell you to shift up, which would of course mean you are spinning too fast with little actual effort.