....Even when an extension does work fairly well and has a responsive support staff, it far too often lacks any good documentation that would allow a user to understand how it works or its impact in context with Joomla and other extensions that may use the same code tools. ....
That is sometimes the case but not always as there are many commercial developers who produce ample documentation and support. They produce the documentation and support for their free extensions as well.
Others provide free extensions but charge for support. It is a material world and there is a limit to how much people can do for free. There is as much variation in documentation and support as there is in quality. The amount of documentation and support is clearly seen before installing the extension.
True some extensions can conflict with others, much in the same way as spare arts for cars(auto mobiles) can. But having a test environment for Joomla, to test extensions on before installing on a live site, will save a lot of problems. Also by keeping a backup then any mistake on the live site can be 'rolled back' within minutes rather than hours or days.
IMHO many of the objections that you raise only have a serious impact on people who plan their site poorly. By opening up your thinking and learning to use Joomla properly you can avoid much of what you are complaining about. When I started using Joomla I had the same problems as you are having. But by learning to use Joomla correctly (as anyone learns to use a new tool) then the problems you refer too no longer are problems.
Again all your reasoning (IMHO) is based on a false premise. The sooner you get the notion out of your mind that Joomla is a quick way to build 'all whistle and bells' websites, then the sooner you will be able to use it correctly.CMS = Content Management System not Build a quick website to avoid time and effort system.
Think of Joomla as tool and learn how to get the best out of it and it might surprise you. I am not 'poh pohing' what you say. And not trying to insult your intelligence. Yes, (just like everything in this world) Joomla is not perfect and there are many difficulties. But by altering your approach then you will be able to easily overcome the difficulties.
If you want a website with fixed content that you need to script and program every change, then keep to your present system. But if you wish to build sites that you can add different features to, then learn to use Joomla as a tool. It took me about two years to understand how to use Joomla efficiently. I can get a basic site up in about 5 mins (or less) now but it takes more time to add what I need. And, as you can see from my site, creating a good 'Look and feel' still alludes me
The ease of using the correct extension comes with experience and the new user will have difficulty at first. But as time goes on and more extensions are tried then it gets easier. It took me at least 6 months to find my way around the extensions directory, and even now there are extensions that I have not tried.
Stop thinking of Joomla as an easy way to build an 'all whistles and bells' website as that is a common misconception. Spend time reading the descriptions etc. of the extensions. Spend time trying different extensions. Try at least 60% of the extensions in each category(that you think suits you).
Once you have tried out at least 60% of the extensions then you will have the experience to voice an informed opinion them. Your opinion is as valid as anyone’s, however it is made without the benefit of years of experience.
Agreed learning the extensions is not easy and requires much time and effort because CMS = Content Management System not Build a quick website to avoid time and effort system.
You thinking that CMS is a quick way to build an 'all whistle and bells' website is preventing you from getting the most out of Joomla.