For the problem of bundle size, it saddens me that Google's Closure Compiler (specifically the advanced mode) hasn't gained much traction. This provides fine-grained tree-shaking to minimize the bundle size. But this requires static analysis of the whole program, which is at odds with the dynamism of JavaScript. Maybe now that static typing is coming back into fashion, the Closure Compiler or something like it will gain widespread adoption.
There's a number of projects out there working to reuse closure compiler bits on top of typescript. e.g. https://github.com/angular/tsickle