Sorry for the long response, my opinion on this is more nuanced than "agree/disagree" and comes from experience training in a number of styles and with a number of instructors (the latter being, in my opinion, the more important factor):
If as the article says you are working with a student who is limited to an hour or two of training per week at most and will quit before a year is up then yes, spending a lot of time on form is probably not going to be your best return on investment within that short timeframe.
However I have two major issues with the article:
1) Equating good form to "vanity" is disingenuous at best. Good form has obvious intrinsic value above and beyond how you look when you are throwing a solid strike. Saying things like "So what are you looking for in your self defense training: vanity or effectiveness?" is very misleading. Good form increases effectiveness, it's not for making you look cool. I don't think I've ever had a traditional martial arts instructor tell me to practice my strikes again because they didn't look cool enough ;) If anything good form is typically stressed from the perspective of understanding and exploiting fundamental body mechanics. This has the benefit of making your own strikes more powerful and balanced, but also understanding and exploiting weak points of your opponent's technique (such as anticipating a wild punch so you can block/counter/throw effectively).
2) Measuring a system's effectiveness by how well it serves relatively undedicated, undisciplined, casual practitioners is fine if that represents the bulk of your students. I understand the need for practicality and to suit your lessons to the level of time commitment you can expect of your students. But that doesn't mean that it is more "effective". It's just better suited to the limitations of your average student.
The fact is that if you are willing to put in the time and effort to train hard then learning good form early is a sound investment of time. Practical defense techniques and good form can be taught in concert. I have studied a number of martial arts and self defense techniques (ranging from the practical to the very traditional) and even in something as traditional and form-focused as Aikido our instructor would happily take time out to discuss, demonstrate and practice how to take traditional techniques and adapt them to make them effective for modern self defense. But that builds on a base of solid form which includes a focus on footwork/posture to ensure that your enemy can't exploit you when you are off balance. Good form gives you power, stamina and balance. I would argue these are the most important things (outside of situational awareness) for any real world self defense system. And yes, you have to spend a bunch of time at the beginner stage practicing stuff that won't help you in a street fight, but once you have that base learning practical techniques becomes easier and faster because you are applying a strong base of muscle memory and adapting it to different scenarios.