Corda supported a decentralized model until 4.x The Corda 5.0 model is about virtual nodes and seems to go away from the decentralized model. How does this dilute the decentralized model where every Party can maintain their own node in the blockchain?
True decentralization is applicable to only an open platform, like Ethereum, where every participant is equal, and has equal opportunity. The Corda DLT platform is built for regulated businesses where well-known real-world entities/parties are allowed to take part in transactions only after granting certain permissions by network operators and agreed upon by consortium members. So Corda DLT is a distributed permissioned network of nodes/vNodes.
The Corda 5 architecture is event-driven, which derives the thought processes and approach from virtualization technology which is the basis for today's Cloud platforms. So, a vNode is quite similar to an EC2 instance in the AWS cloud, where AWS provides and manages the underlying Infra on their user's behalf (IaaS). Similarly, businesses that don't have the expertise or want to offload the Ops risk of managing the Corda Node would outsource it to a trusted technology provider, who can run multiple vNodes as tenants on a single Corda deployment, a cluster, acting as Blockchain As A Service (BaasS) provider.
So vNodes are well segregated from each other, where requests are executed in the Sandbox/sealed environment, and data is stored in physically separate databases.
So when you compare it with the Account model of Corda 4 where the account holder was at the mercy of the node owner/provider. But with the vNodes, a user gets back to the hot seat, reduces the friction in user/node onboarding, and offers progressive decentralization.