Just so you guys don't say the power came from no where later. So far none of Yhwach's abilities have been asspulls given what we know about his birth. He was special enough from birth that humans declared him a god (Yhwach's said to have been given the name of humanity's god and his name could be translated as YHWH as well). All the quincies and shinigamis that have been killed by quincies were stated to have their power absorbed by Yhwach. This also came from exposition earlier.
Now, the previous chapter stated that Yhwach's almighty power is all knowing and all powerful. Unsurprisingly, Yhwach gained two new sets of pupils in each eye. One of the additional pupils in each eye is like the one that allows him to know all (abilities). The other probably grants him the ability to use all (abilities). This would be why he's capable of nullifying attacks. He can comprehend the ability and then use its counter.
Furthermore on whether the soul king exists or not, I suggest you read the last page of Chapter 519 of Bleach. You see the Soul King in the flesh,