Two things wrong with it:

1. People have a hard time remembering the order and which characters to use. The most common error I see is (text)[href]. Spaces in between the [text] and (href) is also common.

2. ( and ) are URL code points: they can exist in URLs without being percent-encoded. This means that you can’t just paste or emit regularly serialised URLs, you also need to change any ( to %28 and ) to %29.

To fix it, you start out by using <> to delimit the URL instead of (). This fixes the serialised URL problem (< and > aren’t URL code points), and it was the traditional delimition of URLs too, where delimition was required. You could say that () was common too, but I’d argue that was just normal linguistic parenthesis rather than URL delimition. Markdown even uses <> as URL delimition already, but only for links with no custom text (called “automatic links” in Gruber’s definition, “autolinks” in CommonMark): “https://example.com” is just text, “<https://example.com>” makes it a link.

As for the way of adding a title attribute to a link, that shows that the parentheses aren’t even actually delimiting the URL. And then you get into the mess that’s […] and […][…], in addition to […](…). It’s an ill-considered mess.

Anything that doesn't force you to remember arbitrary ordering - square brackets first? Or parentheses? It's the textual equivalent of plugging in usb upside down.

An alternative would be to simply use square brackets for both clauses of the link.