> With Facebook, they say they sent more than double the clicks Analytics tells me they sent

This is largely Apple's tracking changes. About 60% of the market is iOS.

In today's world with privacy changes and regulations, you're pretty much limited to econometric time series modeling or A/B testing to understand cross platform marketing drivers reliably. That doesn't really work on 15 dollars a day

With that kind of a budget, it's going to be more worthwhile looking at who is your prime prospect, what is the value you're adding to them and the choice of platform and message follows that.

There's no indication of what it is unfortunately in your post.