It's funny how each VPN has a different speed for all of us. As far as I remember, LoyceV has said that Mullvad is one of the fastest VPN for him while it was one of the slowest for me (especially US servers).
It depends on your location and the load for their server locations.
Maybe for you using one VPN server would be fast, but for someone else in different country this would be slow.
Some VPN services also have different type of connection protocols (WireGuard, IKEv2, TCP, UDP, etc), that can affect quality and internet speed.
Note that fastest is not always the best and the most private.