Thats your natural build and its beautiful. There are many people that are designed this way and some are crushers (Chris Solinsky was jacked). My ex was pretty much your build and took a very rocky road of puking herself and anorexia to become an elite and then she straight up had to end her career for 5 years. I feel like you probably run a lot in the anaerobic heart rate zone with actually makes you more muscular (hince why higher elevation increases muscle mass). I think you should try out different diets and different training styles and see how your body responds. Sometimes you just need to do a month of high mileage at low hr and low protein high fat. Good luck out there