This sounds like a far away paradise.
I just spent a few days revamping the web design of nderground. Getting the externally facing pages to be at least somewhat mobile friendly took a day and a half, working from a template that I purchased.
I find web design a constant frustration. For example, I never could get my internal navigation bars to style the way I wanted.
We are using web technology that is over twenty years old. It was never designed for what we use it for, so web design consists of a bunch of arbitrary hacks (CSS, jQuery, Bootstrap.js, etc…).
On top of all of the pain of web design is the fact that web content never quite displays properly on a mobile device, even if you use responsive frameworks like Bootstrap.
To go beyond an adequate user experience to a good one on a mobile device you have to build a mobile app (in not one, but two flavors — Android and iOS).
Sadly, it seems like we are far away from the paradise that you describe, Richard.