Halo being bigger than anything launching on PS5 in this first year is debatable. There are some big games coming out on the Playstation side which have been huge sellers.Microsoft is launching with Assassin's Creed which is a huge title and Gears Tactics which is new to console. I think those are the two big titles in addition to all the enhanced BC stuff that is free if you own the Xbox One versions or have Game Pass. So to say they're launching with nothing big is disingenuous. Maybe nothing that suits you, but that's another story.
IF you're only talking about the first year then Halo Infinite IS coming in that time frame. And that game is bigger than any other XSX or PS5 title launching in that time frame. Yes, it would have been nice to have it at launch but it'll be there within a year of launch.
Here's to hoping there's some secret games under development coming in 2021.