Btw, I've also been using Sinatra in production environment and deal with large traffic.
And, but is the odd-even, I'm also currently working on the golang team as my main side project :)
the reason why i eventually went away from ruby was two-fold, the primary reason being performance, i was using event machine for asynchronous work, but it felt like it was an after thought, not really that powerful and a bolt on after the language matured. with golang this was built in from the beginning into the language. the second reason, which is almost as equally important, was the deployment, with golang, all i have to do is copy a binary over to my servers, i don't even need a compiler or runtime interpreter, it simplifies my server deployments. but with ruby, i had to leverage rbenv and deploy this everywhere.
i still recommend that folks use ruby if you need something developed quickly that's quite powerful, the libraries are extensive and great, and sinatra is excellent because it gives you the freedom of choice, unlike rails, which i used a lot also, but felt that rails was too heavyweight, it tried to force everything on me.
What you are thinking is very sharp and you will not be able to deny it at least from a fair standpoint.
However, while I write golang, I also love ruby.
Will it be the right place for the right person?
Last, I love the attitude to respect diversity.