Ok, if you can make it purely on the client by checking local blockchain fast and cheap - that's great and should be added.

I am just saying that this doesn't solve anything. You don't protect against typos, because there are plenty of legit cases where address will not be in the blockchain.

Then, you don't protect against unhealthy server at all, because, well, you're a client.

Checksums are used everywhere. Here we are talking about big money and the cost of failure is irreversible loss of it.

Honestly, it's beyond me why are we even arguing this.