Most cons in your list do not have to be that bad:

- Performance: most cms’s are heavy because they have lots of features or are scalable. Buying extra RAM is a cheap price compared to the labor of hand-weriting your own code
- Design: some CMS’s indeed can be very limiting. But not all are. And sometimes you just have to learn a CMS to know what’s possible.
- Poorly written modules and plugins: You always have to watch out for something like that. It’s not always easy, but at Wordpress they seem to do just fine.
- Scalability: I work with Sitecore, which is very scalable and flexible. But indeed, some CMS’s aren’t that scalable, so you have to build something that’s suitable for the CMS.

I agree that external CMS’s have their limits, but I’m still convinced that hand-crafted code is expensive. Use what’s out there instead.

Performance – in most cases (Drupal, Joomla, SilverStripe, etc) cms are slow, resource hogs. Go to the Drupal forums and there are many threads on poor performance, and the answer given is nearly always get more memory, put on APC cache, etc, no one addresses why a page needs 1000+ DB queries to run or why drupal requires 10 times the memory of a custom built cms.

Design – Most (there are notable exceptions, MOdX for instnce) cms are a nightmare for designers to design for, which increases development time.

Poorly written modules / plugins – So great you get this pre-written functionality with modules / plugins, problem is half of them are so poorly written (in the case of open source) that they slow or unsecure, so you then have to check then for yourself.

Difficult to customize / maintain – even the most extensible / flexible of these CMS are a nightmare if you wish to do anything too far outside of their range so you end up with a patchwork of messy code that is difficult to maintain and as for the pain of major upgrades, forget it.

Thank you.