Even a cursory glance at the runtime performance difference between these two frameworks reveals that either this project won't scale to the point that cloud costs are relevant or they have a dubious prioritization of DX over deployment economy. We are talking orders of magnitude fewer RPS for Rails.
I don’t understand your integration of performance and cloud costs here.
“Deployment economy” is also new.
Rails has a very strong track record of matching internet scale.
Cloud is highly optimized for traditional server applications. From my experience with Next.js - this is the opposite. A lot of deployment components that don’t naturally fit in, and engineering required to optimize costs.