It really depends on the type of game and how it presents itself.
Some games have a very long and complex story but others might have a shorter story told more indirectly, then there are also multi-ending games which might take longer than a regular story game since you have to replay them. Then there are sandbox games which don't necessarily have a limit on how long they can be since it's dependent on how much you want to put into them.
Ultimately in my opinion there's not really a required amount of time for completion, the thing that I think is most important is whether the games are fun and enjoyable. In the case of story games they can be as long or short as needed depending on how they tell a story.
Let's be real we should know better. Microsoft isn't doing this because they "care about the community" and cheating. They're doing it so they can force controller licensing and line their pockets. If they're framing it as anti-cheat, that's because they know that it would be better accepted than saying something about "Quality", also it's well known that the gaming community has a tendency to accept practices that would be considered draconian outside of Anti-cheat when it's used as Anti-cheat and will attack those who speak out against them.