Recently, there has been a transition to a microservice architecture, which allows you to write each part of the application using the most appropriate language. If the microservice is not heavily loaded, then it will not consume a large amount of resources and will work quite quickly.
Caching, denormalization of data and the correct architecture allow you to write in Ruby and heavily loaded services. Of course, it all depends on the specific task, and microservices can be developed in languages that are most suitable for solving it.
There is another opinion: the language is already old and leaves the development world. But adherents of this position often simply do not have the information that allows them to recognize the language and framework as a developing and still relevant technology.
Ruby on Rails was one of the first to use the Model-View-Controller (MVC) application component separation scheme, which significantly speeds up the development cycle and allows you to quickly fix errors, quickly implement business requirements in a project, and make changes to them.