We should be looking at this from the same page, as opposed to opposing thoughts.
I too have super flat feet. Flat enough to get me out of the military, 1970, after accepting me for a 8 year hitch and having served almost 13 months!
As you know, people with flat feet can fake an arch given static conditions, and that's how I got in.
I played high school team football and basketball, so I can run.
At 58, I could still run as well as most 30 year olds.
One big sprain of the ankle later, it's light's out....no running, no recovery from an ankle sprain. The pain comes from below the ankle bone. Then 4 years later, pushing my g/f into waves so she could learn to surf, flattenned out my other foot, now TWO "sprained ankles", with little chance for recovery.
Notice I'm 12 years older than you. Beware. I know some old farts who can't walk at all without arch supports, almost dibilitated bare feet.
I doubt all the exercise and PT in the world can help now.
Getting old sucks....getting old with flat feet is worse.