I thought Google Adsense is suitable even for small websites
You need a lot of traffic even for Adsense. A good rule of thumb is 2$ RPM, this is more or less an average that one can expect without any additional data/information. Some niches will pay a lot more, and some less. So now the question is what is expectation or requirement in terms of earnings per month? Say $1000, so 1000 / 2 = 500. That means you need 500,000 impressions per month to reach your goal of $1000.
Impressions come mainly from ranking in Google SERPs, other organic traffic can help, but other search engines bring in a fraction of the traffic of Google, and social media tends to do very poorly in terms of AdSense (there are always exceptions). So you now need to determine how much traffic can you reasonably get from Google, and you also need to estimate how long it will take you gain that traffic.
In an ideal world this calculus would have been done before you started work on your project, to determine if it was feasible or not.
But now the work is already done, the costs, in terms of money, time and resources, spent on development are gone, not coming back. In business lingo, these are "sunk costs". Pour yourself a drink (maybe two) and make peace with that loss. The good news is from that point forward you can ignore those costs.
THEN, use the above to calculate how much revenue you can expect earn from the project, how much you need to invest to keep it alive, to add/improve content, to promote it, to grow it, and then make an educated and calculated decision on whether or not go forward.
The fact that you have Media.net ads running on the website, can provide some valuable information. You can use the RPM from media.net as good gauge set an expectation for what Adsense would pay. Adsense may pay a little more, but don't expect double.
In terms of gaining Adsense approval, I would take not getting approved as a sign that your content quality needs improvement, because AdSense sets a relatively low bar as compared to level of quality required to achieve a good ranking in Google's search results. Phrased differently, even if you were approved today, Google wouldn't send you enough traffic that it would help your situation.
One final remark, making money from ads in this day and age (the age of Google dominance), is not impossible, but it is certainly not easy. You are not alone in your struggles see this thread from a few weeks ago that discuss some of these issues in more detail:
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