I'm working on the styling of a site that uses bootstrap 3. The front-end is not my strong suit, and my role is cleaning up small issues.
I develop my work on a desktop at full-width. We're using the bootstrap pre-defined viewports, and I use that in making a responsive design. Then I check the mobile performance and go from there. Then after that I look at tablet layouts, and it's typically fine. My method perhaps isn't best practice, but it's been working so far.
When I show the results of my work to the marketing client, they "test" various layouts by resizing the browser window they're using on the desktop. By doing this, the page elements are reshuffled by the browser, and can end up in odd places at arbitrary viewport widths.
The situation is that I can't re-create these broken layouts by selecting device parameters in mobile modes. It can only be done by opening the site in a full-size browser window, and then resizing it using the mouse to certain, arbitrary widths.
Marketing is thinking this means that the site truly isn't responsive, and we need to develop it so that the layout looks good at any arbitrary browser width, pixel by pixel. Testing resizing windows would be a break from our current development method.
As far as the site end-users, are resized browser windows really a real-world scenario? Is one of our end users going to get a broken layout because they have resized their browser window (not filling their monitor), or have an oddball resolution on their desktop system? Or need we only develop against pre-defined static sizes?