Cab drivers (who drive automatics) are left-foot-braking all the time, afaik. And I did it too when I was still driving my Nissan Sunny (75-hp-beast with automatic transmission). It just takes some getting used to, and I don't think it has anything to do with strength, just with control and precision.
btw: I would not recommend left-foot-braking in an emergency situation (just think about where your right foot might end up :schwitz