You don’t use event sourcing on its own either. You can use Rails (or Django or Symfony or whatever) to validate the command and add end-user friendly error mes

You don’t use event sourcing on its own either. You can use Rails (or Django or Symfony or whatever) to validate the command and add end-user friendly error messages. Then your models should again validate the command as an ‘anti-corruption layer’, this time throwing developer friendly error messages. That said, I completely agree with your assessment. Event sourcing makes simple things a lot harder. It should be used sparingly, only for those situations when the history is genuinely useful.