I think that there may be a few full-time professional Swing, WPF, ActiveX, Wicket, Flex, ASP.NET, Sencha, WordPress, etc. developers who would disagree with you.
ASP.NET is a nightmare. An absolute nightmare to work with. Sencha (assuming ExtJS) is one of the worst JS libraries you could pick. Not a great deal of experience with the others, so I cannot comment.
That said, there are no doubt good examples using those technologies to do useful things. I am not arguing that widgets make it impossible to create useful things. I am arguing that widgets by their very nature limit what the developer can do. At best you get indirect access to things you need (Application state, Database, etc...) and often times you have no access.
They are the worst form of abstraction. Extremely easy to do one thing. Hard to customize and nearly impossible to do something unintended.
To say that ASP.NET is a nightmare.. I just don't think that's accurate. None of the ASP.NET models are my ideal, and there are plenty of things that can become problematic with the different types of ASP.NET development, but that doesn't have to be the case.
I think that it isn't that hard to have a difficult experience with widgets, but that doesn't invalidate the model, and not all component frameworks are alike in regards to things like ease of extension/modification etc.
Actually in my experience ExtJs is one of the best libraries/frameworks* [1]. It has a steep learning curve* [2] but after that you can build awesome applications quite fast.
* [1] : library based on the author's definition and framework based on sencha's documentation.
* [2] : the learning curve is steep even for experienced javascript developers.
If something is working for you, don't change it. ExtJS is a fairly large framework and replacing it with something 'better' would have a large cost for your organization.
That said, my experience is primarily with coolite and versions 2 and 3 of the framework. I was working closely with another team using 4, which sounded better.
ExtJS' main problem is that it does too much. It tries to replace jQuery, CSS, JavaScript OO frameworks and then adds it's widget/control and code structure on top of all that.
If it just did the last one (maybe two), it would be a decent framework. I still would not choose it because I don't like how it gets in the way of API calls nor the control of event handling in versions 2 and 3. This last point has probably been improved in 4 with the introduction of an actual MVC structure, but I don't know for certain.
In any case, using enormous object literals to configure and control everything from styles, events and actions made it both difficult to work with and test. Often times these blocks of code would exceed hundreds of lines. In short, ExtJS sets up developers to fail. Most of what it does can be written in jQuery using CSS classes far more concisely. It's strongest points were it's UI controls, especially the grids. I think these are the things where the framework adds value, the rest would be better served using more commonly adapted practices.
I think that there may be a few full-time professional Swing, WPF, ActiveX, Wicket, Flex, ASP.NET, Sencha, WordPress, etc. developers who would disagree with you.