A lot of Nasuverse stuff is outdated (but it probably won't be changed for a while, so eh).
Pretty much all of Saber's hax gets canceled out by Doomguy's resistances.
However, Doomguy has a lot of advantages, such as layered mindhax which would probably make Saber increasingly ******** throughout the fight (she has insufficient resistance to Doomguy's layered hax chipping away at her mind and memories),
Saber's Mind Manipulation and Empathatic Manipulation resistances (this should also include Soul Manipulation, Information Manipulation, Conceptual Manipulation, and Memory Manipulation since what they resist affects the soul, and the soul includes all of these, but they aren't listed like this, for some reason) are 6-D from being able to resist Tiamat's and Kiara's Authorities (Authorities are 6-D), her Biological Manipulation and Corruption (types 1 and 2) resistances are 6-D from resisting Tiamat's Authority, her Corrosion Inducement resistance is likely 6-D due to being able to exist within the Abyss (the Abyss is the primordial Sumerian diety, Abzu, so it's inherent hax should also be 6-D, but I don't know if that's accepted), her Life Manipulation and Death Manipulation resistance 6-D from resisting Surtr's Authority, her Law Manipulation and Conceptual Manipulation resistances are 6-D from resisting Authorities, and all of those resistances are layered (Authorities are accepted as layered, but how many layers haven't been decided yet (they could be near infinite layers, but that's not relevant right now)).
She also has extra layered resistance (which is also layered power nullification) thanks to her Rank A Magic Resistance (I know it's called "Magic" Resistance, but it applies to anything supernatural).
eons of experience, a range advantage, an agility advantage (he can sling himself "flying" with the meathook and regularly jumps and strafes all over the damn place), has homing attacks,
Saber does have experience against fairly mobile opponents, but that is an advantage.
has extremely high temperature attacks that go beyond the theoretical limits of temperature (although idk if this applies at this tier),
can stun saber, freeze her, boil her from the inside, has a wide variety of attacks that Saber would struggle to adapt to,
Can that hax bypass 4-D Invulnerability? And can it get past her layered 4-D Power Nullification (though, that might be 6-D since Magic Resistance is listed as working against Authorities)?
and I'm pretty sure he also regenerates faster through healing, which he can do by summoning healing items and fodder (read: walking medkits) by reality warping the surroundings into an arena suitable for himself.
She seems to have Avalon in this, so her regen is going to be similar (she can't die unless her brain is destroyed). What dimensional level is Doom Slayer's regeneration negation.
The arena suitable for himself would probably give him a sort of home advantage as well along with probably throwing Saber off a bit.
That could cause problems, but it depends on what changes occur. How does it work?
Doomguy's power nullification would also weaken Saber
How does his power nullification work? From his profile, it seems like he has to hit them.
and strengthen him whenever he hits her due to his layered absorption. Doomguy also has far superior stamina in case this comes down to a battle of attrition (extremely unlikely).
The absorption might be a problem, but I'm not sure.