When building from npm, and to use local assets there are two steps: (1) copying the assets and (2) configure the asset paths in your code/

It looks like you're only doing step 1. You need to also set the assets path.

The hardcoded paths you're seeing is just the default.

Refs:

• https://developers.arcgis.com/javascript/latest/get-started-npm/#working-with-assets
• https://developers.arcgis.com/javascript/latest/disconnected-environment/