Perhaps I phrased this badly. I don't think the entire article boils down to inheritance vs composition. But in discussing these patterns elsewhere, some of the pushback has been that many Ruby devs prefer to decompose problems via sub-classing instead of composition of command objects, so I tried to cater to that objection with that line.

Pipeline steps are command objects (a pretty standard OO pattern), so they have a single entry point / public method. But they can still fully leverage any other OO pattern in their implementation. The more complex ones I use may instantiate other objects, pass messages between them, etc.

But the single-method #call API is what makes composition easy. See Rack, or any number of middleware-style designs, for other common uses of this in Ruby.