Sounds like an article written by a dive shop trying to sell more gear.
I don't take issue with the idea that you're using the right tool for the right job, but in the case of sidemount (your bone of contention it seems), you're actively saying that it is a poor choice for MOST things when that's certainly not the case.
I'm not quite sure what "many more drawbacks" you feel exist when someone exclusively dives sidemount. In fact, the "drawbacks" you listed are specious arguments at best. Slower? Nope, I know guys who dive sidemount that are the fastest guys on the boat. In fact, since most sidemount divers are generally more experienced, most sidemount divers are faster than inexperienced divers in a stab jacket. Inappropriate for wrecks? Nope, I know guys that almost exclusively dive wrecks almost exclusively in sidemount, they don't have any problems. Sidemount is absolutely better for low stuff, that doesn't mean it's inappropriate for other situations. Shouldn't dive an exclusive system so a dive shop can sell more gear? Sorry, BIG FAT NOPE. A dive shop doesn't exist just so that I can keep them in business. I owe nothing to my dive shop, they exchange products and services in exchange for money, that doesn't mean I owe them anything extra, like buying extra gear that I don't need simply to have another piece of gear lying around that may or may not actually be useful given my particular diving habits. Dive shops are businesses, not charities. The fact that most dive shops would gladly sell me redundant sets of gear under the auspices of making sure my "toolbox is complete" is a sad reflection on the state of the industry, and I am under zero obligation to support them simply to keep them in business.
Your "toolbox" analogy is poor. Diving isn't a case where the world looks like a nail when all you have is a hammer. Sorry, it's just not.
I think you're doing the opposite of making diving enjoyable by recommending they buy more gear. How often do we say that you shouldn't use a gear solution for a skills problem, and yet this article espouses exactly the opposite, for the benefit of the dive shop, couched as some BS explanation that you're doing the customer a favor.
And this is coming from someone who has never dived sidemount in his life, and the closest thing is slinging deco bottles on a buttplate and bungees.