Indeed. Was trying right to zap some monero and it is as you describe. It is basically a normal transaction outside the platform, with privacy assured is difficult to get that functionality here.
I guess that would only work with an integrated wallet on this platform that can validate an 0,00X amount being sent. I wouldn't mind that and just send some monero to that internal wallt for tipping around nostr.
But yeah, we need a better way to zap in different currencies.