This article confuses the term HIT (high intensity training), a strength training protocol) with HIIT (high intensity interval training), a cardio protocol.

Other than that, yes, HIIT is an effective cardio protocol, and much research has shown that intensity matters when it comes to cardio.

What's discounted here is the full picture of fitness and training: cardio alone isn't sufficient, especially as you leave your 20s and 30s and suffer age-related muscle loss (sarcopenia).

The pretty cool thing about effective training programs is that significant gains, and certainly maintenance of a pretty high level of performance, can be attained on fairly minimal training. Three times a week, 10-20 minutes of cardio, and 30-40 minutes of lifting (less if you stick to big compound lifts) can do a huge amount for general fitness. Some abilities take longer to train -- especially skill sports. But the body is amazingly adaptive to constructive stress.