While all of the activities just mentioned are great for strengthening foot muscles...
And relieving or even reversing many chronic foot conditions....
The one that works best of all is sprinting. Or better yet, barefoot sprinting.
Ironically, the reason this is true...
Is that it is perhaps the most physically brutal activity you could ever do on your feet.
The first few times you do it, your feet will likely feel even worse.
However...the body is smart...
And it will learn very quickly that the old way of doing things with soft cushiony shoes...no longer work anymore.
And the only way to make easier the next time...
Is to start actively using your foot muscles the way they were naturally designed to be used.
And just like any other muscle group, they will get stronger day by day...
Until eventually whatever foot problem you struggle with becomes a thing of the past.
Of course, that's not a guarantee, as the list of potential foot problems is quite long.
But I'll still say, your chances are pretty damn good. So give it a try.