If you are referencing the world instance (which is bound to this) in a step definition or hook, then you cannot use ES6 arrow functions.
Cucumber uses apply internally to call your step definition and
hook functions using the world object as this.
Using apply does not work with arrow functions, so if you need to reference the world, use a regular function.
Why do my definition patterns need to be globally unique instead of unique only within Given, When, Then?
To encourage a ubiquitous, non-ambiguous domain language.
Using the same language to mean different things is basically the definition of ambiguous.
If you have similar Given and Then patterns, try adding the word “should” to Then patterns.
When Cucumber runs your specifications, scenarios are collected and turned into test cases. The features that those scenarios sit within are not considered in the test run - it's all about scenarios, which should be standalone and not depend on any other scenarios. This is why Before and After hooks are available at the global and scenario levels but not the feature level.
If you find yourself wanting to do some setup work at the feature level, consider whether you can move it to the scenario level and make it idempotent. You can target a hook at all scenarios in a feature with tags.