: "Highly compressed" installers frequently include hidden miners or trojans.
: This is the primary home for the game. Steam uses its own compression during download, so you usually download about 40-50 GB, which then unpacks to the full size.
If you find a site promising a "500MB" or "2GB" version of Vermintide 2, it is likely a scam or a virus.
: If a friend has the game, you can copy their steamapps/common/Warhammer Vermintide 2 folder to your PC. Steam will verify the files and you won't have to download anything.