It is true that you can have a Negative Income Tax that has the same outcome, in terms of disposable income, as a Basic Income. I explained the situation in this article:

..so I do understand what you’re talking about.

But even then, there are important reasons why Basic Income is superior to a Negative Income Tax — as explained in the article.

The security that results from knowing exactly how much Basic Income you will receive each week is more than just a ‘technicality.’

Furthermore, in practice, the withdrawal rate of welfare payments tends to be much higher than income tax rates. And this withdrawal of benefits is often applied in addition to income taxes. I don’t know what the withdrawal rate is for the benefits you are referring to. Perhaps you can tell me?