What makes a private route actually fast
The route out of the country is the part that breaks. Encryption is easy. Routing is not.
Most VPN comparisons focus on encryption protocols. That is the wrong layer to focus on.
Encryption is solved. Modern ciphers are fast, well-understood, and run with negligible overhead on any device made in the last decade. Two VPNs using the same protocol will have effectively identical encryption performance.
The difference is the route out of the country.
What a public VPN actually does
A typical low-cost VPN buys a few servers near the border, runs a public protocol, and shares each server's bandwidth among thousands of paying users. At off-peak hours, this is fine. At peak hours, the shared link saturates and every user on it slows down at the same time. There is no per-user fairness, only a shared queue.
This is why a VPN can speed-test at 200 Mbps at 3 AM and crawl at 5 Mbps during a 7 PM video call.
What a private route does
A private international link is a contract with a Tier-1 transit provider for guaranteed capacity on a specific path. The capacity is not shared with the rest of the internet. The route is not subject to the public BGP politics that make public links unpredictable.
Capacity costs money. There is no free version of this. Which is exactly why most VPNs do not bother and explains the speed gap users feel.
What to look for
If you are evaluating a VPN for serious work, the question to ask is not which protocol it uses but how it handles peak-hour capacity. Vague answers usually mean shared public links.