Those things put seperatly Steam is far from the best option , except for the store part because that’s their main thing.
The launcher part is just part of Steams basic DRM, some games can be started from their directory without Steam running.
The subreddits and Discord servers for certain games are usually more organized, cohesive and feature better fan made content than Steams Community Hub.
Nexusmods is far superior to the Steam Workshop in every single aspect.
For Reviews most people go to YouTube and watch a video. Steams review system is more an indicator of general reception rather than actual gameplay.
Steam doesn’t try to squich all the other platforms they just provide a convenient alternative to them. So why are all those things suddenly an issue.
How do you even enforce breaking all those things up? Should there be a law that all governments agree on, that states Steam exclusively can’t host mods anymore? Should they be split up into subsidiaries, like Steam Store, Steam Community, Steam Mods etc.?