Ruby on Rails is still the most productive why to build web apps. Turbolinks prolonged Rails life cycle, as the best web framework, by two or three years.
However SPA are the future. Maybe Angular 2 will be good enough to switch. Maybe something build after Angular 2.
Probably because you haven't really provided any supporting evidence for your conclusions. Always show your working out. (Also, for many people, the first thing they do on a Rails project is disable Turbolinks.)
I actually happen to agree that Rails is still a supremely productive way to build certain types of web sites and/or applications. An experienced Rails guy, leveraging the vast array of gems out there which can solve many different problems with just a few lines of code, can get an MVP out of the door extremely quickly.
Two years ago I built an app using Angular. Of curse using Rails as the back-end. As a whole this wasn't a good experience. A such simple thing like authorization took a day or two to implement, solution looked like a one big hack.
However some SPA/Angular features worked beautiful. Two way data binding and local templates allow to build complex forms very easy. Data validation of one to many associations was straightforward. In Rails we have to use accepts_nested_attributes_for. It is so 'nice' that some people want to move nested attributes functionality to an external gem.
The biggest thing Rails is missing: components. There is a discussion today on HN [1] about this. Angular, web components, HTTP2 might really allow to build real object oriented web apps. In Rails there is a view.erb file and that's it [2].
I guess that competition will force developers to build even more user friendly and responsive apps. By that I mean no more separate pages to add a simple record. New apps will allow to click on a record, edit it in place and save with enter. And to do that well we need SPA architecture.
However SPA are the future. Maybe Angular 2 will be good enough to switch. Maybe something build after Angular 2.