> the amount of tools you have to pull in these days just get some single page interaction going...
I just started contributing to an open source project with a lot of JavaScript without any modules or even IIFE wrappers, everything is global. Just 1 year ago I would solve the problem with a new build system but now I'll just gradually introduce ES6 features, and I will not do any module refactorings because in 6 months I can probably just introduce standard modules without any build step.
When modules ship, 90% of what you need for a SPA will be available natively in browsers. If you are building a complex product, complexity will naturally increase, with build steps for various reasons.