>Experience seems to be what's holding him back in this case.

We can only say that it's "holding him back" only if we can show that he doesn't get the same results as SASS users, in the same amount of time.

They are not same results. One code base is monolithic and hard to maintain while the other is modular and simple to update and maintain.

This critique presupposes what it was meant to prove.

There is no argument. Simple facts. Plain CSS is monolithic and hard to maintain. Disprove it if you want but I think you'll be hard pressed. This author did not succeed.

You presume that he needs to change but give no reason to do so other than you think your way is better. He says his is better and a lot of people, including myself and a well-publicized recent article, feel the same way.

We think your path is the wrong way and will cause you problems as time goes on.

Speed, maintainability, modularity and readability are all good reasons. I'm sure that there are many more reasons but these are just off the top of my head.