The SOULs being opened venerable to attack can be read as opening up their inner being, which includes their dreams, when translating over to Hollow Knight.
This means the Knight has no SOUL.
So, only Lightners or Humans can attack Vessels.
Also, let’s assume a cross between both worlds for the arena, and every version of every person fighting.
Godseeker spammmyies Absolute Radiance.
Gerson and Sans dodge everything.
The Failed Champion and False Knight rage and spam attack the Knight, who is physically flattened.
Absolute Radiance and Shade Lord would be a Fair match(a bit unfair, actually) to him
Also Ultra Omega Final Super Duper Absolutely Insta-Kill Beam of Angel of Hyperdeath Asriel would take the two to the 0.000000000001 of their first mask
And, if 19946491472748382 Monster SOULs are equal to 1 Human SOUL in DETERMINATION, then what about 99999999999999999999999999999 Void SOULs?
Remember the Shade Lord is a Mega-Amalgamate of all the Shades
And the true extent of all the Void in the universe's Power is unknown, but if a dream can literally materialize, then they are the God of Gods.