I do not agree. Rails is absolutely great in terms of features and productivity, but will fail you elsewhere i.e. it is not the silver bullet for webdev. Do not take my opinion, look at data - https://www.youtube.com/watch?v=Qp9SOOtgmS4
If you are using Rails for anything where you are not absolutely sure of how many users or RPS you will have, you are just saving money in launch time but spending more on servers.
If you are using Rails for anything where you are not absolutely sure of how many users or RPS you will have, you are just saving money in launch time but spending more on servers.