Maybe you need to change the post title to am i mentally capable of being a great fighter?, form your post you seem like a determind person dont let flat feet stop you becoming a great fighter. I think it was joe frazier who was almost blind in one eye and he didnt tell anyone for fear of loosing his Boxing license and he more than held his own.
Hope the exercises below help you physicaly

The Exercises for the treatment of Flat Feet are divided into two main groups:
Non-Weight Bearing (Sitting) and Weight Bearing (Standing).
Non-Weight Bearing Exercises.
Sitting: active foot rolling. The patient tries to draw an 'O' with his/her big toe. For the right foot clockwise; for the left foot anti-clockwise.
Sitting: trying to pick up a duster. A duster is placed under the foot, and the patient tries by using both feet to screw the duster into a ball, then inverting (raising the internal arch of) both feet, he/she tries to throw the duster into the air and catch it. Similarly the patient can be encouraged to pick up balls, match boxes, etc., with the feet.
Sitting with strong extension of the knees: dorsi-flexion, holding them in position.
Sitting: alternative toe clawing. The toes of one foot are actively flexed as far as possible, gripping the floor and pulling the heel of the foot two or three inches forwards. The toes are extended, and the opposite foot is similarly exercised. In other words, the toes pull the foot a short distance along the ground. Care must be taken to ensure that the patient does not push the foot along using the leg muscles.
Sitting: sliding the sole of one foot up the leg of the other.
Sitting: foot shortening. The foot is slightly inverted (the internal arch is raised), but the sole is not turned upwards. That is to say, the height of the arch is increased, whilst the toes are still gripping the ground.
Sitting: foot-closing. An attempt should be made to close the foot, like a fist.
Sitting: toe adduction and abduction. This means the toes are pulled away from then towards one-another.
Sitting with both feet crossed and inverted. Holding them in position.
Weight Bearing Exercises.
Walking on the outer borders of the foot. Each foot should be lifted over the other one at each step.
Standing: heel raising and lowering to the outer borders. The patient starts with the feet inverted, raises the heels, and lowers the outer borders.
Standing with the feet inverted. Holding this position.
Standing on a book: the edge of which is placed immediately under the metatarso-phalangeal joints. The toes are then flexed and extended.
Standing: foot shortening.
Walking along a straight line.
Correct heel and toe walking:
The patient is taught to walk with the feet along parallel lines. Any tendency towards slaying must be immediately corrected. The heels should first be placed on the ground, the outer border next, the toes finally.. The weight should not at any time in this procedure be taken on the inner border. The heel is then cleanly raised from the ground, the five metatarsals used as the fulcrum, and the big toe for a concluding propulsion to a straight leverage. The heel and toe walk brings all the muscles into equal action, and ensures normal balance.
All the above exercises should only be undertaken when the patient is rested and not tired.
The amount and frequency of the exercises would be decided by the patient's Chiropodist.
Disclaimer: We do not recommend that you undertake any of these exercises without proper consultation with a qualified professional. These are for information purposes only.
You do them at your own risk.