Yes and no. Onion is similar to IO-less Rust or "Functional core, imperative shell" in that it goes one step further from inversion of control/monadic effects a

Yes and no. Onion is similar to IO-less Rust or "Functional core, imperative shell" in that it goes one step further from inversion of control/monadic effects and removes all control/effects from the inner layers. You get some benefits like being able to write very straightforward business logic, but in return you: - have to constantly fight the entropy, because every day you'll have to implement another corner case that is 2 points if you violate the layer isolation and 10 points if you reengineer the layers to preserve it - have to constantly repeat yourself and create helpers, because your API layer objects, your domain layer objects, your DB layer objects all look very similar to each other. Sometimes a transaction script (in Fowler's terminology) with basic DI scaffolding is easier both to write and maintain, especially when the domain isn't rocket science.