"If you mean by setting `position: absolute` and then using left/top/right/bottom to position your element, that won't work."
Erm, but it does? You can listen to resize events and you can get the exact width and height values of all the elements in the DOM. I am using that technic since I switched to the web (when box layout did not exist yet).
The only problem with this is, that you can create performance bottlenecks easily, as reading clientWidth might trigger a forced reflow. So it might not be easy at first to get everything right, but it is totally possible.
Also you can just use a different GUI framework or build your own.
"Not everyone's goal is to simply have as many users as possible."
Mine neither, but those who do (the majority) made sure, the web is suitable to be used by even the most tech illiterate people.
My mother can surf the web to get mostly what she wants - but she cannot use a file browser, nor does she really know what a file is (and she does not want to know).
"> The app you make, you can ship by simply sending a link.
Depends on what it does."
Sure, if you want native file system access, you would be breaking the sandbox. And yes, this is my biggest pain point with the web as well - that it often cannot decide whether it serves untrusted websites or enables app developement where the user trust the app. For example there is no (easy) way to get the pixel data from html elements, because of security. Which makes sense for malicious add filled websites, but not when developing something real, where the user could give permission. Here the focus on the dumbest users who just all allow everything, so the browsers have to protect them and allow no one to use proper permissions is really annoying. Because yes, I also would just like to have file access and other things permissions don't allow.