Hydraulic disc brakes require less pressure on the lever to engage the caliper, so one finger has more than enough power to stop you. And it allows you to keep three fingers on the handlebars. Modern brake levers are also designed to be used with the index finger, and when properly set up, you can comfortably ride with this finger in the ready position on the lever.
If you're using two fingers on your hydraulic brake levers, it's probably time to reconfigure your set up for one finger braking. Move the levers inboard so that the curved part near the end of the brake lever sits under your index finger. You shouldn't have to reach for it or change your hand position on the grips.
Check out Vital MTB's cockpit set up guide or chat with one of our techs to learn more!