What does "at scale" mean? I ask because my last job was at a web host with 80,000ish paying customers. We had over 100k users of our web portal (built with Rails) which customers use to manage their sites. This was a business with over $100 million ARR around when I left last year. The user portal is the primary point of contact between the business and it's customers and we never had serious issues "scaling" Rails. It was a totally fine tool for the job.