The blog correctly explains how it has become pretty useless in our age where noone writes their own database integration anymore and everyone uses off-the-shelf components, but man... I remember a time when it felt like literally every sufficiently complex web service was vulnerable to sql injection. You could write a small wrapper for sqlmap, hook it up to the results of a scraper, let it run over night on every single piece of data sent to the server and the next day you'd have a bunch of entry points to choose from. It even handled WAFs to some degree. I'm out of it-sec for several years now, but I still remember every single command line argument for sqlmap like it was yesterday.