By siloed I was referring to all the VB-style apps that predated widespread use of the Web. You had to use a single mediocre client app because it was the only piece of code in existence that could support the proprietary protocol for the matching server. Lock-in was rampant and building a better client or repurposing the data in any way was almost impossible.

Now we have servers that may technically still be talking XML or JSON or something over HTTP, but it might as well be an opaque proprietary protocol, because there's only one piece of code in existence (the javascript embedded in some page) that knows how to send meaningful requests to the server or decode its responses. The protocol isn't even stable enough to reverse-engineer because the author can make arbitrary changes to it and migrate everyone to an updated version of their client code at any moment. I find this vastly inferior to query strings, multipart/form-data, and scrapable semantic HTML, which a growing number of web devs completely neglect (none of whom I'd ever hire).

> should browsers not support JavaScript?

They shouldn't run it by default without asking whether the user trusts the author. Privacy violations are rampant and even malicious scripts have become a recurring problem. I don't see why a sandbox that works shouldn't be possible, but it hasn't happened yet.