I don't know where you got your information...but you can achieve wire speed with OpenVPN over a 1gb link. If I had a bigger pipe, then I could run a bigger test, and expect the same results. The rest of your points fall under "it's not easy for average users" - which I agree with.
That depends on how much horsepower you have on both ends. I run my vpn off of a cheap cloud vps, which does the job, but doesn't have a lot of cpu power. I probably tripled my speed from openvpn to wireguard, all though both fail to max out my internet connection.
