This is such a massive simplification of what a designer does it's actually amazing. You're first and last paragraphs are simply wrong. First of all a designer

This is such a massive simplification of what a designer does it's actually amazing. You're first and last paragraphs are simply wrong. First of all a designer doesn't get to live exclusively in photoshop or some other tool. They don't get to ignore the "reality of usage". In order to be a competent designer they have to not only completely understand the problem domain, but also the given software solution and how a user can use the software to achieve the desired goal in the most concise manner. They have to worry about how to signal to users how to perform any given interaction and the overall complexity any activity has. Also they absolutely do test designs with real users. There is like a whole field of study in design around exactly this. As to your last point, drawing != designing. Designing is actually really hard. This is a problem I see with programmers all the time. The oversimplification of others contributions. Yes you can put together a UI with drag and drop tools. You can build a website with drag and drop tools too and you'll probably get the same quality as the drag and drop UI. A drag and drop design will probably have most of the various pieces. But will it be obvious what actions a user can take from any given screen? Will it properly optimize screen space, and be color correct? There are a 1001 questions that a designer has to ask that most programmers wouldn't even think to ask. There are many challenges when writing an app, and good design has proven over and over again to matter just as much to the success of a business as solid code.