I think you are correct that "You do not understand Google ads", at least from the perspective of how it affects your YouTube traffic. You put gas in your YouTube car when you paid for Ads. The gas ran out and now you are confused as to why the car is not moving. It is not that difficult to understand, but I think your issue is not that you don't understand it, but that you did not get the result you expected. Here is what I think is bothering you. You can correct me if I am wrong.
You thought that if you paid for some ads, this would get some momentum going on your channel and that momentum would generate a snowball effect that would continue to travel and gain speed even after you stopped pushing it. Am I hitting close to home on this? I think I am. Unfortunately, when you stopped pushing the snowball, it did not keep going and it just stopped dead. So, what does that tell you? Here is what it should tell you. You were not pushing the snowball down a steep enough incline. Let me explain.
You thought that paid promotion was a shortcut to get your channel going. Paid promotion is a powerful tool, but the key is, you have to have a great product too. If you have great promotion promoting a not-so-great product, it is not going to get you anywhere. What your experience with Google ads has revealed is that your channel does not have to appeal to keep going on its own. You did not do the groundwork to get your channel ready for paid promotion. You were pushing the snowball uphill, so to speak. So what is your takeaway from this valuable experience?
1. You need to invest more time in building your channel organically before you try paid promotion again. If it won't grow on its own, it is not gonna maintain momentum if you try to grow it artificially with paid promotion.
2. Make sure that when you do decide to pay for promotion again, you have everything in order to capitalize on it. You want the skies waxed with silicone and ready to go down a black diamond. When those paid ads start bringing in new customers, you want the bait and hooks to keep them on the line.