Steam didn't employ forced retail exclusivity.

You also don't seem to be fully aware of Valve's contributions to Linux gaming.

Valve grew Steam’s market share by locking in exclusives.

By exclusives you mean their own games? Or are you referring to the time before Steam Greenlight?

There were multiple digital distribution platforms in the early days, IGN even had one.

Yeah I remember D2D, it had awful DRM and they deleted my account one day without refunds.

Then Valve forced exclusivity to starve out the competition.

No the competition died because they were trash. I used D2D, Origin, Impulse, they were all horrible compared to Steam.

Steam has its Most-Favored-Nation clause to prevent publishers selling games for cheaper on other platforms.

No, Steam doesn't let you sell Steam keys to your game on other platforms for cheaper. That's very different.

Valve fought against refunds for years until the EU told them to wise up.

I refunded things multiple times for the policy changes. As long as you gave a good justification and weren't abusing the system then they have always been quite reasonable.

Valve only started supporting Linux when needed to sell consoles. They just like most other companies saw Linux gaming as an extreme niche.

No this started because of the Windows Store initiative back in 2012 where Microsoft was trying to consolidate the sale of all software to their proprietary platform. Supporting Linux was Valve's way of hedging against that future.