I have no experience with Telerik at all. But it’s shocking to hear such things.
In the past (from 2012 to 2015) I have been using DevExpress components for .NET. They also have webcomponents, but I have never used those either.
But since I started using Aurelia (since this year), I doubt that I will ever need any of such commercial 3rd party component libraries at all. I do not need them for my current development projects anyway.