This is a commonly suggested potential wincon for Chief, here to rain it down.
So basically Chief has two antimatter weapons, the Incineration Cannon and Binary Rifle. They aren't UNSC weapons so he won't have them often, they're also not covenant weapons so it doesn't have the iconic status like the energy sword. They are Promethean weapons, something he only really fought between Halo 4 and 5, and beyond that the Binary Rifle and Incineration Cannon were rare for Prometheans, basically appearing like twice in either of the actual games.
Furthermore, the Incineration Cannon projectile only moves at
48.37-68.90 m/s which Doomslayer can easily dodge. Regarding the Binary Rifle, when aimed at by the rifle, the target receives a bright glare to alert them, so Doomslayer is gonna realize Chief is using some weird weapon. It then helps that
Doomslayer also has an energy shield for his chaingun (that can also do damage) which is bad news for Chief because
even in the Halo games, Hardlight Shields can resist Binary Rifle shots.
Actually now that I think about it, that also means the Hardlight Shield from Chief serves as a half second defensive roadblock against Doomslayer. It might be able to resist a ballista shot, but once again it's Promethean tech and while more common than the Incineration Cannon and Binary Rifle, still won't be as common as something like the Drop or Bubble Shield he uses a lot more. Doomslayer also has area of effect weapons like rocket splash damage, grenades, the BFG, etc so won't matter.
Furthermore, it's not like 1 gram of anti-matter touches a person and annihilates all 60 kilograms of that person. It annihilates 1 gram and as a chain reaction creates an explosion which mass scatters the rest. The Promethean anti-matter weapons aren't even pure blobs of anti-matter, they're coated with anti-matter, which means a low mass. Realistically the vaporization we see in game isn't the total body being annihilated, it's a small part of the target's matter exploding so hard it vaporizes the rest. The issue that Doomslayer's armor can survive the argent tower explosion and Vega's detonation, kiloton level events. So like ignoring that Doomslayer can just outrun and dodge the Incineration Cannon and detect and block the Binary Rifle with his energy shield, even if they hit he might get a bit of his armor annihilated, but he's so strong the ensuing chain reaction explosion won't do shit to him.