Use javascript to loop through all images within bbcode designated areas and size them down to a maximum specified size if required.
If you know how to use jQuery, you'll be able to do this in well under half an hour.
Sorry, but if you don't think that Wordpress is a CMS, you obviously don't know what a CMS is.
Whether or not it's default functionality is extensive or broad as you'd like or not, it does not preclude it from being a CMS.