https://www.bbc.co.uk/bitesize/guides/zf9g4qt/revision/1#:~:text=Christians%20believe%20that%20God%20is,the%20world%20to%20human%20beings.

"Christians believe that God is omnipotent. According to Christian belief, God created the world and everything in it, and also continues to be involved in the world, sustaining it. In the Bible, there are many accounts of when God demonstrated his power and involvement in the world to human beings."

Many people do seem to believe that God is omnipotent. Otherwise, why are they praying to him and living according to his supposed rules in fear that he will do something to them? So I was arguing against the existence of the type of God that most people these days seem to believe in.

A more accurate version of your analogy would be: many people seem to believe that purple cows exist. I've seen no evidence of purple cows, and I have some reasons why I don't think they exist.

"The idea that God is omnipotent, instead of just really really powerful, is actually a fairly late development even in Christianity. I don’t remember the exact date, but it was sometime during the late middle ages."

So they noticed that he didn't seem to be in control of eveything and updated their beliefs accordingly? Well, I suppose that's something at least.

But the term "really really powerful" is vague. What is he able to do? Is he able to answer prayers? Can he kill evil people? Can he cure diseases? Can he stop devastating forest fires and floods? Can he get people out of poverty? I mean, what the the bloody hell is he actually doing up there? Because the way things are right now, no stretch of the meaning "really really powerful good supreme being" even covers it.