Some of your points I agree with, some I don't, but there are at least 150 million hardcore gamers out there playing on PC, PlayStation and Xbox systems as we speak. It's a sizable target group.
The whole point of Apple entering that market with a gaming system would be this: it would be much easier to start developing and publishing games for that audience instead of just relying on mobile games played on a big screen. There's already a number of "hardcore games" on the App Store, an Apple "gaming console" would attract more developers capable of delivering such games.
It's also worth noting that if Apple indeed decided to bring out a gaming system, REGARDLESS of anything else it would easily sell 5-10 million units just because of the company's loyal customer base (fanboy base?). That's a good enough userbase to build on (and sell Apple Arcade subscriptions).
So it's not inconceivable for Apple to go ahead with a plan like that. If I had to guess, I'd say it's more about whether the company can expect the high margins it is used to in other product categories, plus whether it finds the role of a platform holder attractive or not. I'd really like to see them take a stab at it, though, just to upset the current status quo in the gaming market. It could use the shake-up.