Given how trivial it is to set up serverless Rails using something like ECS Fargate, the benefit of running specifically on Lambda is lower than migrating off a tried and tested technology.
With ECS Fargate it costs money even without any traffic and you are responsible for correctly implementing auto scaling.
I'm coming from 10y rails dev background and now full stack typescript. Thinking in pure lambda functions is a breath of fresh air for me.
Like everything, no? This is akin to saying "All tautologies are tautological."
Your sentence preceding this one laid out some issues; you probably could have left it at that <shrug>.