Interesting your flat feet doesn't bother your legs at all....
Mine are a completely flat footprint, so no arch whatsoever.
Been doing sports all my life, but especially running on the beach as a kid.
I can probably name a dozen or so professional athletes whose career was ended by foot problems....and they had flat feet to start with.
I also can name twice that who had great careers in sports despite their flat feet, but now retired, have problems walking or running with advancing age.
I can also name at least a few people who've done OK all thru their lives, until reaching retirement age, and now their flat feet totally screw up their sports lifestyles.
Guess it's not an exact science.