Ad revenue is not a good indicator I believe.

Ads are expensive for most advertisers (when you calculate cost per acquisition) and cheap for most content creators. The main reason is there is too much advertisement trying to catch attention, so it is race to the top for the advertisers, but actually not much is sold.

Ads as a revenue model works for the top mass-market creators (think pop stars), it usually does not even cover the costs of (online) magazines.

Most content creators actually make money by either affiliate programs that can be targeted better (but not always - for example the endless VPN ads in podcasts), or by selling the content directly.

I don't think it makes sense to compare ad revenue to zaps as the only thing, because that is not how most content creators actually make money. Ads sell attention (in somehow unrelated way to the content), while zaps should capture the value created by the content itself.

If I create interesting content and get paid for showing you an ad for hair shampoo, it is not related to the content. The point of value4value is to value the content itself, not your attention around the content.

So I would personally rather compare zaps to how you can monetize content and not how people monetize attention, which sounds similar, but it's actually a very different business proposition.