I read many of the analysis on towards deciding for a base framework for my next project. Here are the conclusions;
(PS: I am heavily coding in WordPress for the past one year, and I am an experienced web developer and software architect for more than 18 years)
Argument 1 - 'WordPress is a CMS / blog engine, but not an application framework'
It is like saying 'Microsoft is a technology company'.
Which is simply not TRUE. (Yes, Microsoft creates good technology, but it is a marketing company. E.g.: Its competitive edge is not creating the best technology on earth, but pushing what it does successfully on to business decision makers.)
WordPress is a solid application platform and CMS/blog functionality is the default application that comes in the box. I think the main reason why WordPress is under estimated as a development platform 1) custom post types / custom fields functionality is so new; we haven't seen enough applications benefit these features. 2) A very high percentage of the WordPress community is non-technical people (designers, bloggers etc.) compared to other 'low-level platforms' such as CakePHP, CodeIgniter, etc. So the non-WordPress developer community is not aware of what WordPress can really do.
Argument 2 - WordPress is not based on MVC so it is not a credible development platform.
Sorry, but it is not TRUE.
MVC is not new-age religion that everybody should follow. Yes, it simplifies debugging, development with it structural approach to coding. At the end of the day it is an approach (among many others) to make your life easier as a programmer and save you company's valuable investment embedded into your code.
Plugin architecture and theme based UI-logic isolation in WordPress is quite enough for many purposes...
If you still insist on using an MVC approach you can do it; WordPress MVC like plugins.
Argument 3 - WordPress is slow and it is not scalable for high-traffic web sites.
Not true.
Yes, WordPress is slower to render a page compared to your hard-coded PHP code, (due to additional process execution overhead). BUT if you are relying on your code rendering performance in order to high scalability, sorry, you don't know anything about scalability.
WordPress comes with a zillion caching and performance plugins that will deliver a better site performance that you can hardly match with your own effort.
Final conclusion;
I don't want to be the 3,434,533th developer to build a login/password recovery functionality for his/her web site. This is why I go for WordPress.
At the end of the day, our time is limited in this world.