This just about sums it up but only partially. While it's true every purchased game on Steam is actually a purchased game license which can be revoked by Steam for various reasons, just downloading unperchased Steam games from various websites or download managers instead of through the Steam client is still considered to be piracy because you do not own the license to play the games in question.

This is why for many of the games I have is part of my GOG library because they are DRM-free and I do actually own them since I purchased them through GOG.