In your first example, the creation and initialization of the public instance field named defaultValue in Child occurs after the creation and initialization of the public instance field named value in Parent.
So: even though the this value in the initializer of the public instance field named value in Parent will point to the instance of Child under construction, the child-local public instance field named defaultValue does not yet exist, and so the prototype chain is followed up to the property named defaultValue on the instance of Parent, yielding 1.
In your latter example, you have getter functions named defaultValue.
Getter functions specified in this way, even though their API deliberately looks like that of public instance fields, will end-up as functions on the [[Prototype]] of any instance under construction.
The [[Prototype]] objects of instances are created at the time of class declaration (ie. always before anything triggered by instance construction), as the .prototype property of the class (or constructor function); references to these objects are then copied to the [[Prototype]] of any instance under construction as the first step in object construction (think Object.create(class.prototype)).
And so this.defaultValue from the Parent public instance initializer for value resolves to the getter on the [[Prototype]] of the instance of Child under construction, which is a function that returns 2.