Whoever said they're useless because they're multi?
They're useless because they're not good as Sony games.
That's purely subjective, I mean, 10MLN people wouldn't play a game on a daily basis if it was bad, would they?
Also people will play them, doesn't mean someone bought a XB1 over a PS5 for them, and they didn't.
But that's completely irrelevant in this entire software-based business, you sell 10MLN consoles, 20, 50, 100, a billion, it doesn't matter, you don't make a profit anyway, but if you sell 1mln, 5, 8, 10, 15 copies of a game, the numbers do stack up
Granted PS5 and XBSX have GTA, COD, Fifa, Madden, Mortal Kombat and Assassin's Creed, can you see many people getting a XBSX over a PS5 because of Halo and Fable?
Yes, those games are exactly the reason people chose cheaper X360 over PS3, and cheaper PS4 over XB1, not because of Halo or Fable, if anything multiplatform games are the best examples why 1st party games don't matter much, especially in times where it takes 5-7 years to make them, so they don't come earlier than 2nd half of the generation, an there are only so few of them, there's a reason both hesitate so much to show off their price tag first.