High Anonymity proxy server
You don't need hundreds of proxy servers to get high anonymity. Services like TOR and ProxyMesh provide high levels of anonymity by changing IP addresses periodically, instead of using hundreds of proxy servers all at once.
Rotating IP Addresses provide High Anonymity
What makes a system like TOR or ProxyMesh highly anonymous is that the outgoing IP addresses are not the same as the proxy server you connect to, and more importantly, the outgoing IP addresses rotate. TOR changes paths every 10 minutes, which is much faster than ProxyMesh, which rotates IP addresses every 12 hours. However, with ProxyMesh you get 10 IP addresses at once, and a much faster and more reliable service, because it doesn't route you around the world. So if you're concerned with being as anonymous as possible, use TOR. But if reliability and speed are important, you can choose ProxyMesh Rotating Proxy Servers and still maintain a high level of anonymity.
Static Proxy Servers are Less Anonymous
Other proxy services tend to focus on the quanity of proxy servers and IP addresses they can provide. However, these are static IP addresses that do not change. You often get a fixed number of IP addresses, and cannot change IP addresses more than once a month. It's much easier to get blocked using static IP addresses than if you have dynamically changing IP addresses, like you get with ProxyMesh and TOR.
Another reason a proxy service may focus on quantity is because the proxy servers are less reliable, and so you need more of them to make up for it. Some services just provide lists of open proxies, which are notoriously unreliable, slow, and possibly malicious.
Hundreds of Proxy Servers are hard to use
Large quantities of static proxy servers are also more difficult to use. You need to have special software, or go through complicated configuration and programming to access all the proxies at the same time. Compare this to the ProxyMesh HTTP Proxy Server or TOR, which both implement common protocols supported by practially all client software. ProxyMesh even supports IP address authentication, which makes configuration even simpler.
The bottom line is that getting a high level of anonymity does not require hundreds of proxy servers. You can be much more anonymous with a rotating proxy service like ProxyMesh or TOR. And these services can even be cheaper, faster, and more reliable than services that advertise huge quantities of IP addresses.