The people who would typically buy COD have moved on to other games and are playing those
instead. There is no world where those people will be buying Battlefield/Arc Raiders in addition to COD (should COD manage to ever not be the same recycled shit again), that's not how it works when that crowd only buy 1-2 games per year.
So no, in this current real world scenario where COD's numbers continue to fall year after year, the only party who suffers is Microsoft since they are the ones who now own Activision.
The other 3rd party platform holders retain the users that would otherwise have purchased COD, and they retain the dollars spent since those people will spend the money that once would have gone towards COD on other titles.
Despite your hopes and dreams for a fictional scenario where the risk is spread and has a contagion effect on the entire industry (or in particular towards Sony, which is funny in itself considering they are not the only other counterparty in such a scenario), the results prove that it is Microsoft alone who have taken on all the risk, and they are not getting any reward.
Sorry for your delusion, and sorry for your loss.