Assuming you can legally operate on both A and B in your country, isn't it a matter of sending your $3750 from B to your bank then depositing $3750 from your bank to A? Obviously that step alone (fiat B => bank => fiat A => crypto A) could take well over a week before fiat in B is back to crypto in A.

I know I'm missing something because a lot of people a lot smarter than me are in this space. I just don't know what it is I'm missing from the outside.