It isn't providing the evidential basis, it's providing the legal basis. Ie the signature isn't used to authenticate in a public-key cryptography kind of way, i

It isn't providing the evidential basis, it's providing the legal basis. Ie the signature isn't used to authenticate in a public-key cryptography kind of way, it's being used as a legal trigger: 'if you write a name here that isn't yours, you are committing a criminal offence'. (How that offence is proved is a separate issue). Hence electronic signatures can be as simple as typing your name into a text box (or even just a checkbox). The (dubious) uniqueness of a handwritten signature is nonessential.