VPSes usually have "virtual CPUs", meaning they are shared between people who rent "virtual CPUs" at that hosting company. When you have a Raspberry, you most certainly have a dedicated CPU. This makes a big difference in terms of consistent performance, you always know how fast it can go and won't suddenly perform worse because your "neighbor" on the VPS hosting is also using a lot of CPU.

This is also why dedicated instances are usually way better for performance-sensitive hosting compared to beefier VPS instances.