I get the concern. I haven’t seen the pattern used in practice in an OO context, so I also can’t say for certain where this breaks down. Something to note, though, is that object algebras in an OOP context are equivalent to the final tagless pattern in an FP context, and it’s not uncommon for entire functional applications to be based around final tagless. This gives me some level of confidence that it would only take a reasonable amount of discipline to build a system based on object algebras.