etc, etc. Even back when I used telerik components, it was often faster to develop my own component, tailored to use-case, than it was to figure out how the hell to customize the 15-deep DOM tree that a table component generated.
I agree. Telerik (and similar) components are great for getting you a lot of functionality straight out of the box, with minimum time and effort.
Where they break down is when you need to make any sort of non-trivial customization or business-specific use case. At that point, it's easier and more maintainable to build things from scratch, or with more loosely coupled base components.
For React: http://material-ui.com/#/
Bourbon + Refills: http://refills.bourbon.io/
Material Design Lite: http://www.getmdl.io/
Bootstrap: http://getbootstrap.com/
etc, etc. Even back when I used telerik components, it was often faster to develop my own component, tailored to use-case, than it was to figure out how the hell to customize the 15-deep DOM tree that a table component generated.