Good questions. Yes, Apple Arcade is a direct competitor for games as a service. While the technology under the delivery is different (games are downloaded and then played), it offers a direct competing service to xCloud and Stadia since they are all based on a subscription model, and if the library and priced matched, they would be nearly identical services, bar the delivery (one streamed, the other fully downloaded digitally).

It's not clear whether these services need to be playable on iOS to succeed, but Apple has 30% of the global marketshare, and in the united states it has 56%. The others could possibly succeed without being playable on iOS, but it cuts potentially 50% of their audience, which at the amount it costs to offer cloud gaming, could make it an unprofitable proposition, esp. in the US where all 3 companies are headquartered.

The task of submitting games for Apple's review doesn't pose a barrier, but could result in abuse of power by Apple (which is the case with OP), and allows Apple again too much power in dictating what is playable on these streaming platforms, something it never required from other non-gaming streaming services.

It begs the question, is this preferential treatment due to Apple trying to block competitors on its OS? It all points to yes.

Do you really want to say that the standard for approval on iOS is higher than on Gamepass?

I meant Apple might not approve of the content. Maybe it's offensive.

In terms of standards, Apple might not want laggy, streamed games to become thought of as typical of how all games play on their platform.

Could definitely be interesting.

However, in this case Microsoft and Google are direct competitors to Apple for streaming game services. The others not so much. Since the apps being blocked are purely streaming service, on that aspect alone it could be anti-trust and a means to block competition. We know what happened to Microsoft when they played foul with Netscape, I'm surprised that this kind of thing isn't being taken seriously nowadays.

And, if the courts are not taking care of it, at least people should be bothered by it. In the days of Netscape, Microsoft was public enemy #1 for its behavior. Today people seem complacent with this kind of monopolistic practice, I think it's a bad sign.