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"Always do X" and "Never do Y" are almost always bad advice. Live by rules of thumb but don't become a zealot or rigid purist. Some duplication is acceptable, but lots is probably a sign that something is factored poorly or the wrong tool for the job.

Rules of thumb include but are not limited to: KISS, YAGNI, and DRY.

Another good rule of thumb is make things easy to figure out for future maintainers who you have yet to meet and may never. Programming is communicating with a future human, not just a machine. It's about people. (Insert Soylent Green jokes here.)

At least in ordinary CRUD, I find that simple, re-composable mini-components get me far more reuse than big swiss-army-knife-like components. Small components that can be copied, tweaked, remixed, or ignored with ease are more flexible.

Also, communicating via strings and string maps (dictionaries) makes them easier to mix and match than complex data structures/classes. String maps are relatively simple yet flexible for structure passing. You lose a little compile-time-type-checking by going string-centric, but there are work-arounds, such as optional named parameters that switch on type scrubbing when needed. (I love optional named parameters. Every language should have them.)