It seems you are missing the point.
You are having outages because your hosting provider detected that your account is using too many server resources.
You are using too many server resources because you are serving too many ads.
If you are serving too many ads and you are not making money enough to cover your hosting costs, that is solely a business problem.
Any ad server, not just OpenX, will take you a lot of server resources once you start serving too many ads.
You can perform some optimizations in shared hosting account but you will still be limited in the number of ads you can serve before you take more server resources than your hosting companies allows. There are no miracles.
Of course, if you know what you are doing, you will be able to perform some optimization tricks even in shared hosting.
The problem is that many users do not have enough knowledge to configure applications and servers to make them be efficient resource-wise. So, for those, hosted solutions are better, independently if they are free, because they do not have to learn anything too technical.
This is a common business model of many Open Source companies, not just OpenX, but also Wordpress.com among many others. Being Open Source no longer matter for those users because they will not take any direct benefit of that.