This story is really sad - I would not have wanted to be in your place when you told your client or investors that you wasted 30.000$ on nothing and that you need to start everything from scratch, with another system, with another crew. I think there is a lot to learn from your story.
First, there is no system that is a good choice for "any task". Plone has its strengnesses and also some drawbacks: it is an excellent choice for many solutions but as you point out too, it is not good for anything.
Second, it needs expertise to develop with. It is a common mistake to believe that experience arrives without an effort. A good developer needs to be more of a craftsman then of a genious, and yes: plenty of learning and practice is required to become a good professional and carry out a project of the size that you referred. This stands for any system, although the learning curve of different systems may differ - as do the services they provide as well.
And last but not least: personal choice has an important role, too. If, for example, you found "python notation .. terrible; verbose, clumsy, the white-space requirements .. completely ridiculous and impositional, ... an obsolete language" (- end quote): then you should not have started with python at all. Luckily, there are more excellent languages and choices out there, and it seems you could find the right choice for your taste in the end - although you learned it the hard way.
The good news is for any future potential users of Plone is: that they don't have to pay the same price as you did. There are virtually hundreds of companies and individual consultants around, who are more then happy to give professional advice to companies who start with Plone - including advising you against it, in case your project is not fit for Plone. Plone also has an excellent developer community with a mailing list and irc channel, and I am quite convinced that if you had spend some time on asking your questions on these resources, you would have get more then friendly answers, and these answers would have saved you from most - if not all - of your later problems.