Is joomla and Wordpress really for designers, or should I write my own cms?

Is joomla and Wordpress really for designers, or should I write my own cms?

Having designed websites for years, the idea of moving to a cms and
simplifying content updates is appealing, especially as it gives the
customer the ability to manage some of their own updates, but am
struggling to get the design control into joomla or Wordpress.
I've purchased Artisteer and still seem to be moulding my sites' design
into artisteer as opposed to vice versa.
Am now considering writing my own cms and wondered if people had any
thoughts. I don't want to design the cms for the masses, just me. Have
very good php, MySQL skills but have heard about ruby on rails and need to
work out the balance of learning something new or sticking with php.
Thanks for any thoughts or opinions!!