Since Steam is a form of DRM itself does that mean that ALL games on Steam, even the ones that are not “online-only”/“rely on central server” will be marked with “You are buying license only” message?
Steam the launcher itself lets you download the games.
But Steam DRM is entirely optional, it's up to the publishers to use it or not. There are countless games on Steam that you can download and play without DRM (say copy to other PCs without Steam and play there)
I see, hmm… So, pardon me, just want to make things clear.
I can download game through steam, then copy the entire downloaded directory to external drive, copy that game directory to another computer, “double click game.exe” and play the game?
Yes, if the game doesn't have its own DRM or use Valve's (this is admittedly mostly older and indie games these days). You can even use it to manage/sync games/applications that aren't distributed on Steam: https://help.steampowered.com/en/faqs/view/4B8B-9697-2338-40.... I believe this will actually sync those files to Valve's servers and allow you to install them on other machines with Steam installed. This was a feature to drive adoption in the very early days of Steam when basically all it was good for was downloading Counterstrike patches.
Since Steam is a form of DRM itself does that mean that ALL games on Steam, even the ones that are not “online-only”/“rely on central server” will be marked with “You are buying license only” message?