Yeah, because of situations like this i said that you need to have been training for quite a while to form a good idea.
Your an endurance athlete, wich basically means that your entire body is build to conserve energy at the most efficient rate, where as in the weight room, its about short keeps of force and rapid recovery.
For your situation, its normal that your bench is behind. For a distance runner, every ounce of muscle on triceps and biceps is to much, because you dont need it and dont use it. Same with shoulders in lesser degree.
benchpress comes from chest and triceps primarely, and shoulders secondarely (when done right).
Do you want to improve benchpress ? Because it will not be optimal for your running performance.
Split squats... I misread it. You mean as in Bulgarian split squat ? where one leg is locked (on a chair for example) and you bow down the other leg ? because that excercise, is mainly on the quadriceps. "half squats" (wich i tought you said), are also mainly on the quadriceps.
if you want stronger calves, i got a pretty efficient excercise for that : standing or seated calf raises.
standing : put a piece of wood on the floor (3-5cm high). Put about 70-100 kilogram on a bar (including the bar(=20kg)) and go stand on it with the front cussions of the foot. Your feet are now in decline position. Now simply lift your heels as high from the floor as you can , and decend back to original position.
alternative : use a leg press. fully extend your legs on it. put the feet on the bottom of the plate, heels under the plate, only front cussions on it. now do the same movement but horizontally
Steated. (best with machine cause of hurt). Put a piece of wood on the floor. sit on a bench and place feet on the wood touching it with your front cussions. put a bar with 50-60kg on your legs,close to the knee. now lift up the bar by lifting your heels of the floor, leaving the cussions on the wood.
25 rep sets. You will feel the burn if the weight is right. Dont start to high.
Sidenote : many gyms got a machine for this
seated calf raise
standing calf raise
alternative