A lot of exchanges' policies on handling finance seem to have stemmed from a very simplistic idea that funds you invested in crypto must've come from a bank account or touched a local account (perhaps making it safer for them to comply with regulations).

I don't think the only option they should be giving you is to prove your source of funds with a bank account if you can use other sources or have historic transactions that backup your activity (although why you'd need to do this at all instead of just proving your identity doesn't really make sense).