Boring does not mean bad. Postgres is boring. Ruby is boring. Ruby on Rails is boring. They are good and well understood. Their failure modes are well understood.
Polyglot programming is sold with the promise that letting developers choose their own tools with complete freedom will make them more effective at solving problems. This is a naive definition of the problems at best, and motivated reasoning at worst. The weight of day-to-day operational toil this creates crushes you to death.