There are a couple of things that bug me when talking about vanilla js and "scalability".
The first is that no one is making the argument that frameworks aren't built with vanilla js, so it seems silly to bring that up.
The second is the notion that being famous is synonymous to being scalable. Github, for example, isn't a great example of a "scalable" frontend: think about it, where do you see anything more complex than showing/hiding a widget? Compare with something like Google Maps or Google Docs and we can see that there's a world of difference in the amount of client-side complexity involved.
This second point goes both ways though. A good amount of "web apps" are more similar to Github than they are similar to Google Maps. There's definitely some merit in the idea of using classic server rendered frameworks like Rails + JS augmentation, as can be seen by the increasing popularity of SSR among the popular SPA frameworks.
The first is that no one is making the argument that frameworks aren't built with vanilla js, so it seems silly to bring that up.
The second is the notion that being famous is synonymous to being scalable. Github, for example, isn't a great example of a "scalable" frontend: think about it, where do you see anything more complex than showing/hiding a widget? Compare with something like Google Maps or Google Docs and we can see that there's a world of difference in the amount of client-side complexity involved.
This second point goes both ways though. A good amount of "web apps" are more similar to Github than they are similar to Google Maps. There's definitely some merit in the idea of using classic server rendered frameworks like Rails + JS augmentation, as can be seen by the increasing popularity of SSR among the popular SPA frameworks.