Email-to-Case allows administrators to set up routing addresses that automatically create cases from incoming emails and assign them to queues based on predefined criteria. This way, emails from customers can generate cases automatically and be sent to the correct queue. A flow is a tool for building automated processes, but it is not designed for email routing. A custom email service is a way to process inbound emails using Apex code, but it requires coding skills and is more complex than Email-to-Case. Anescalation rule is a way to escalate cases based on certain conditions, but it does not create cases from emails or assign them to queues.
References:https://help.salesforce.com/s/articleView?id=sf.customize_email2case.htm&type=5