Having a UI Designer tool greatly streamlines the UI design process for most developers. Designer tools help developers visualize what they are creating, and write some of the code for them. But if you already feel productive hacking that code by hand, more power to you.
XAML is probably the closest thing to language-independent UI that Microsoft has. Given the "many languages" paradigm that Microsoft adopted when they created .NET, XAML was a natural choice. You can manipulate a XAML UI just as well in VB.NET as you can in C#, or any other .NET language, for that matter.
What you see as complexity in a designer is mostly necessary. Each control on a form may have 40 to 50 properties, ranging from event bindings to size and location in a container. Having this level of complexity insures that you have the necessary flexibility to mold the UI to your particular vision.
The real choice to be made is not the designer per se, but the underlying technology. Do you choose a proprietary but mature interface like WPF, or an open standard like HTML5? The designers, from what I've seen, are not all that different from each other. They all have property pages, design surfaces, etc.
I personally would shoot myself if I didn't have a designer. Even the simplest of Windows forms involves dozens to hundreds of lines of boilerplate code, code that I don't have to write by hand if I'm using a designer. A simple example of something you don't want to have to code by hand: the position of a control on a form. Why estimate the X and Y position numbers when you can just drag the control to the proper position on the form, and have it automatically line up with other controls or snap to a grid?
Actually, I'm a huge fan of code-generating a UI through templates. Creating a detailed UI is very tedious for most software developers, whether you're using a designer or not, so if I can hand some code generator a table or series of tables, and have a template code-generate a sensible UI for me, why not?