The problem is the "just switching" typically means a full rewrite and has a ton of logistic challenges. Are you gonna higher an entire second team? What happens to feature work on the current system? If you keep going full-throttle on features, you'll never catch up. If you stop developing features for a prolonged time, you are putting your entire business at risk.

Writing new services in Java might help, but still doesn't solve the main issue if your Rails app is a monolith. Breaking up the monolith might be a bad decision and is also super expensive and might even eat lots of the potential performance gains.