You can argue a monopoly only where there are both an active actual monopoly and when there are anti competitive practices in place.

Steam doesn't do anti competitive, their 30% cut is actually a deal when you consider how much you get in comparison to Epic or Gog, who both take 30% but both offer considerably less. Valve doesn't push for exclusives the way Epic does and valve doesn't do anything to make you not able to publish to other stores at all.

Their edge is that they offer a better service for the same price.

I don't think I agree. Steam is a distribution service and it's up to the publisher to decide if they're going to use AI in their design. The use of AI content is so wide and applicable to gaming from the code to art to marketing etc that it's absolutely unavoidable that large publishers will decide to use it.

Starting ~~in 5 years~~ today, every major game studio will be looking to use AI to cut costs, and if steam blocks this content, they'll be left behind quickly. What happens when Unreal, Unity and even GameMaker or Godot are utilising AI generation (or aren't but Adobe already is and their programs are used in many parts of game design already). Do steam block 90% of major and minor developers? What happens when a game is made without AI in an engine that was made with it, or marketed with buzzwords from a language model.

Any distributor who blocks AI generated content is embracing rapid obsolescence. Hell, any publisher who makes a lot of money from independent developers such as Sony will be risking becoming obselete by outlawing AI, as many of their developers would likely end up using AI and moving to other publisher's as contracts ended. P

Sadly these companies are competing with other companies who are willing to do whatever it takes to make the most money. As a distributor, if the publishers is using AI, they need to permit it or die, as the publisher, the same goes for the developers, for the developer, the same goes for them to the game engine developers, or the art software, or the presentation software in their development strategy briefings. If remaining competitive is part of your companies goal, which it probably is, then you basically need to let AI into your production wherever it shows itself as more convenient or die.