You should do what makes sense for your DCs of course, parental choice is a wonderful thing and not everything will suit every child. BUT - I wouldn't base a decision for your DCs today on anything in this article, and I don't agree that it's good on what prep schools are like now. Not only have things changed vastly since Charles Spencer was at prep school in 1972, the author even notes that his descriptions of his own prep school getting on for two decades ago was already a fossilised throw-back: "By the time I arrived, in 2010, these institutions had been confused into taking one of two paths: rapid modernisation or entrenchment. Mine chose the latter, and that made little sense."
It's clear that the prep schools that exist today in 2026 were the ones that unlike the one in the article did choose rapid modernisation, hence there are hardly any full boarders at age 8 left and those that are are overwhelmingly from abroad. The article's description of what "boarding is like" bear little resemblance to what any parent is likely to be dealing with today. Also, while boarding at 8 has almost vanished, boarding at 11, 13 and 16 are each a different proposition, at different developmental stages, and so "choosing boarding" is vastly different whether you start at 8 as a full boarder or are weekly or flexi, or indeed a boarder starting as a teenager at 13 and coming home every weekend, or every 3 weeks for an exeat.
I think it's also clear that what prep schools were grappling with in the runup to 2010 vs today has changed significantly with the advent of screen time, social media and phones. There are a lot of parents who are now looking for ways to give their children a screen-free or at least a social media or phone free childhood and schooling, with what we are still finding out about anxiety, depression and attention disorders possibly associated with children and unfettered screens/phones/social media. So what he portrays as a backward, old-fashioned emphasis on getting kids outdoors in 2010 is now actively sought out by parents in 2026 but is often only possible in prep schools, or by parents who are engaged enough and have enough free time to supplement their kids' schooling with sports and outdoor activities, if they are at schools that have sold off their playing fields and grappling with resources cut to the bone.