Of course I would not accept it as a valid argument because it is BS. The appropriate argument from lightning is: If lightning existed in ancient times, then the source of lightning, which is electricity, existed in ancient times, even though no one at that time had a notion that electrons and electricity existed. Are you going to dispute the logic of that statement?
In terms of a God hypothesis we need to start with the definition of God that God (YHWH) gave us. God said, "I AM WHO I AM." Exodus 3:14. This indicates that YHWH has unlimited power, wisdom, and love, which makes YHWH uniquely able to have created the universe out of nothing. This agrees with Genesis 1 and John 1. It also corresponds to the facts of the Big Bang Theory, which makes it clear that the universe does have a Beginning and did not create itself.
The God Hypothesis is important to science, because it means that the universe is rationally structured which is basic to the scientific project.