Fixing the mess that is wordpress is a very nobel goal.
The ones you can buy however are a nightmare for sure, so are most of the copy-pasted-glued-together ones.
And where wordpress really shines is in the ecosystem. Subscription list popups, SEO, social media integration etc are just a few things that clients commonly want that take far less time to integrate into wordpress than building from scratch (because it's fairly common that authors of less popular developer-centric CMS'es didn't think to implement those things).
In my experience, WordPress is not built for developers or designers. It's built to be simple and extensible from the end-user's point of view. Most end-users don't expect absolute perfection and accept that it will do 90% of what they want. As long as it keeps doing that, no one will care what a "mess" the insides of it are.
That's the generous interpretation. A more jaded reader might have started reading the article thinking 'mention of Angular... 3... 2... 1... ah there it is! suggesting node... 3... 2... 1... ah there it is! Well at least he managed to contain himself until the next to last paragraph'.
It's technology-centered myopic navel-gazing. Yeah nobody uses Wordpress because PHP in templates is not 'clean'... Oh wait, half the world does use Wordpress because everybody and their dog has a server with PHP and because it's dead simple to hack up something working by cramming some PHP into a template you bought for 5$. For 95% of all websites, who cares about maintenance? Just do a new one in 3 years with whatever is hot then.
This article (and many like it, not singling this one out) reads like people who call themselves 'real' woodworkers, lamenting that people won't fork over $2500 for a hand-crafted oak dining table and instead get a $100 Ikea one. The popularity of 'Ikea hacks' amongst the crowd that tends to author articles like this is ironic in that sense...