A fully-isolated VPS is better than a shared server for WordPress because it offers dedicated resources for vCPU, RAM, and storage. With a VPS, the resources are completely separated from other users, reducing the risk of security vulnerabilities. An isolated server also provides better performance and more control over the server environment, which is crucial for managing a WordPress website with custom configurations and resource-intensive plugins.
In contrast, when other sites on a shared hosting server use up the shared resources, it can cause performance issues for all the sites on the server, including slow page load times, server downtime, and even crashes. Since all the sites on the server share the same resources, such as vCPU, RAM, and bandwidth, if one site experiences a sudden spike in traffic or resource usage, it can impact the performance of all sites on the server. Additionally, if a site on a shared server is compromised due to security vulnerabilities, it affects the security of all the other sites on the server, putting them at risk of data breaches or malware infections.