Actually, template engine is usually not about backend language, but rather a DSL of the template engine language...
For some reasons, template engine DSL is much more popular than simply string interpolation, or lit-html, for example, for the backend.
Also, what is usually slow, is the communication between frontend and backend.
front to backend takes time yes. But what takes more, an html template, or react + components. And react/vue/angular/etc do take more bandwidth on the first load. Granted yes that is only once. This part I think is the minor part of the issue at hand. What is more complex, the html templating, or react with components.
Granted I am still learning react, most templating on the server side is dead simple. React and others are way more complex.
My point, is that all that complexity to me, so far, is for nothing. when templating is way simpler and using react adds the complexity and much more code to debug, test, integrate, etc. And the more thing that can break.
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