The checksum is not meant for you and your eyes. It is meant for the application so that whenever a user enters the checksum incorrectly into that tool's textbox it can automatically detect if there were any mistakes in the input so that the application can inform the user that something is wrong.
but we still need a way to make sure we wrote it down correctly. and you just admitted as much. since just by looking at 12 words, you can't tell whether there is any discrepancy in them or not.
Some wallet usually ask their user to re-enter partial or all 12/24 words generated on previous step of wallet creation.
also, they'll definitely know something is wrong whether the software detects it or not. when their balance doesn't show up.
True, although it'll take more time.