I fly out of MCI and rarely give them 2 hours. Only 2 things slow down international check-in when your first leg is domestic from what I can see- first, AA doesn't let me check in on-line for international flights, so I need to make sure I'm not there so late my seat is given to a standby. Second, an employee needs to check your passport and, if you're going someplace that requires it, your visa. I was once encouraged to use the check-in kiosk at MCI for an international flight and-surprise- at one point it stopped dead so an employee could verify my passport.
In general, my answer would depend on how crowded your originating airport tends to be at your departure time. If there are nightmarish "security" queues, get there early, domestic or not. MCI is a gem in that respect.