This data is present on Overwatch disc but simple install isn't working probably - setup installs Battle.NET first and go to the net so he ignores disc data for install.

Found only JavaScript utility to read data but python script or exe utility will be much prefred one - https://github.com/Kruithne/node-blte

Small part of disc data for possible analysis - https://dropmefiles.com/JP8aX

CascView and overtool cannot read this data - first requires build.info at least and other work with already installed data only.

You'll probably need to write your own script. CAS is designed to be read as a whole (root manifest -> encoding -> index -> data) which is why all the tools and libraries require a full installation/Blizz's CDN to work

Simc have a python implementation for reading the CAS containers including BLTE parsing you could reference - casc_extract source