I cannot pretend to speak for System Error Message, he is a particularly smart person and can explain himself just fine. But what I *think* that he meant by "...you need a proxy too" is that a proxy diverts away from the VPN connection itself, which obscures you from the VPN provider.
In other words, if your VPN is a corporate connection to your work, then obviously it isn't private or anonymous, it is just (hopefully) secure. And if you are using a commercial VPN service for privacy, your connection is still not obscured from the VPN provider, regardless of what they say. You are relying on that provider's history of resisting subpoenas and the like and kinda crossing your fingers. In a way, you are using the VPN provider *as* a proxy, and using something else in between those two connections may make it more complex to locate you.
The rest of what he is saying about Tor being government controlled, and about not being able to pick your own nodes, I do not understand. There are absolutely malicious actors running exit nodes, and many are likely state sponsored, but you can configure nodes in torrc.
Connecting to a VPN server through a second VPN provider has a speed penalty, but is a better idea than through a proxy if the intent is to make it slightly more difficult to identify a VPN user. But why is he writing “proxies have the additional benefit of being able to manipulate your request? What benefit, in this context?
Here’s another way of using a proxy together with a VPN: as a kill switch.
SOCKS5 proxy
Use our SOCKS5 proxies to further minimize your computer's identity from being revealed and reduce CAPTCHAs.
mullvad.net
Does Merlin kill switch have to check with the server every few seconds to verify there’s an VPN connection, and if not, cut the link? If that’s the case then a proxy as a kill switch seems more secure since it passively cuts the link. Mullvad’s proxy is on the same server as their VPN.