requires going through the desktop interface to install them, if they use another launcher you have to set up that, frequently some trial and error

Valve does pre-compilation of shaders. That only works for native Steam titles, and it can be the difference between a game being playable and a stuttery mess, especially for more graphically intense titles

there are also hardcoded patches in Proton that look for the SteamID of the game to apply them. Those also won’t have those fixes applied when adding them as non-Steam games.

How is any of this the fault of the World of Goo devs? How come Valve shouldn’t be expected to implement features to make these things simpler/work?

Modification and distribution of modified copyrighted content, if not permitted, can be a copyright violation

Generally you are not distributing any content from the game. Most mods to games are using API calls to a mod loader to change the game for the user on runtime. These distributed mods generally have no copyright content in them.

The problem here. Is that they’ve already started working on DLCs before the game has even launched. You don’t see a problem with that from a consumer standpoint?

Sort of a complicated scenario. Where do you draw the line for it being anti consumer? Say the people on the dev team who do: concept art, writing, modeling, etc. What should they be doing. At this stage most of the development going into the game is very final touches (if that) and bug squashing. I don’t think it’s out of line for those people to be working on future content. Seems a bit strange to hold them until the release date. It definitely is a tough line to find though, and can change depending on the context of when and how the dlc development started.