I think that kind of process, slow decomposition based on performance and requirements, is the only sane approach.

It's also reflected in how we manage code at the micro-level: collecting related logic into a module until it becomes unwieldy and then separating out independent sub-functionality into their own modules and dependencies as they grow...

There is no right size for a class. Smaller is better, but the ideal is "right sizing". What's right? Well, that's tricky, but whatever doesn't hurt is pretty ok.

There's no right size for a service. Smaller is better, but...