Edit: (just noticed that these brifters are for road bike, probably a non-issue then. This issue seems to be more mountain bike related)

Sounds like cantilever vs V-brake lever issue to me. Like you had cantilever and changed over to V-brakes without changing the brake handles (which are very brake style specific) or maybe you have cantilever and changed your front brake/brifters out for something different that use a different style of brakes.

Your brake levers need to match the style of calipers you have. If you have cantilever brakes, your brake handles should reflect that. Same with v-brake style, you need v-brake levers.

if you have the wrong brake levers, then you will adjust the brakes to their are almost rubbing and you will have a solid feel but the brakes just won't stop like they should.