That article is from 2012. Admittedly a lot of people moved off for the pricing reasons but essentially everyone I communicate with in the US uses SMS/iMessage today.
That seems to be a US-specific oddity. My German mobile plan still charges per SMS (a few cents per message), and apart from verification codes or delivery notices, I never receive any SMS at all. No one uses them for personal communication over here, to the point where people don't know how to send them and I wouldn't know of another country apart from the US where SMS are still widely used.
I'm French and SMS are ubiquitous here; sometimes even more so than email. All operators offer unlimited free SMS, even the cheapest 2€/month subscriptions. I'm not sure I personally know anyone who uses WhatsApp.
SMS used to be priced like you describe until a new operator (aptly named "Free") entered the market in 2012 with free SMS plans and forced the other three operators to align.
Whatsapp is (and especially was) way better at sending photos than whatever SMS app installed on one's phone. It also used to work with crappier phones, for which there was no easy way (that I know of) of installing a SMS app that would send photos. Plus, you have Whatsapp private groups, which I don't know if you can emulate using SMS.
I use Gchat at work as essentially an adjunct to Gmail. I don't even have any of the other apps installed. I do use Facebook Messenger for one good friend who lives in Europe.
But, in general TBH, I don't use texting all that much day to day.
