Look at the caliper/rotor from above and observe while squeezing the lever...Does the rotor appear to twist or bend with contact from the pads? Caliper may be misaligned and the mounting bolts arent secure. If no, then possibly friction in cable housing from mud/crud. Maybe dripping lube onto the bare wire near caliper with bike upside down (allowing lube to run down wire into housing) will loosen it up some. If it does then Id consider replacing it with new to bring the original feel back.
Seriously doubt its the pad wear after only 250miles esp. since you say the lever is hard to squeeze.