So Yeah Zillow has an effect. It's worth it to create a login & enter in your upgrades, so your ZESTIMATE goes up.
Very nice, thank you, my Zillow estimate is now $5965 higher. We have no intention to sell but if we do, at least I can start the negotiations at a higher price point by pointing to Zillow.
Of course, if I compare my house to actual sales in the neighborhood over the past few months, that's probably 10% high, so correcting Zillow's data about my house made the zestimate less accurate, not more.
But yeah, your conspiracy theory nonsense is probably just as legitimate.
I did it before Zillow, and they start with the property value as estimated by the city for tax purposed and look at recent sales that are similar in the area, and adjust.