Rollup, indeed, is a next generation ES6 bundler and does a lot of magic. I am using now it everywhere.
You really don't need to put so much code (at least how Angular provides its architecture) for modern SPAs (which is actually a modern buzzword for DHTML, this technic existed for many years) and you don't need SPAs everywhere like everyone's trying today.
Browser is still browser, mobile network is still same sometimes very slow network, HTTP is still the same HTTP, you don't need to do "back-end engineerig client side". JavaScript was made for scripting browser and it is the simpliest language in the world... well untill back-end developers came to frotnend and started overengineering it trying to simulate classes, interfaces and everything else you really don't need in JS.
For MVC there is very lightweight library http://mithril.js.org/ and a lot of simplier alternatives on GitHub and even 20-line routers.
For template engine, which is 2kb and x100 faster then React - I have found this awesome project http://monkberry.js.org/
There is also my own approach, which is still far away from production release, but you can get main idea from the index page - https://bunnyjs.com
Browser always will be a simple static page, where you need to init some of custom components only when needed. You have a datepicker, you included datepicker - a standalone lightweight library without dependencies, you need a search, dropdown, autocompletes, tab switches, form validation, datatables, ajax (or feth API now), whatever else - again you just include a small package for that. That's why jQuery was so popular and still is - simplicity. With ES6 actually there are so many new web APIs that I can do a lot of things in few lines of vanilla JS.
My favorite comment on the medium article I provided - "Abstraction is great but nothing beats vanilla JS."
Main probolem of front-end today - "The Gorilla and banana problem".
I am also sorry for "funboyism" and you are, of course, right, it always depends on what you need to build.