Content Management is defined by Wikipedia is a set of processes and technologies that support the collection, management and publishing of information. Content management can apply to any form or medium such as a single document, group of documents or a website.
Coding a website by hand using HTML is a very exact process. While the results may be phenomenal they can also be time consuming and very costly. But the benefit of designing and coding a website is that it offers greater design flexibility over using a content management system. It also allows you to add style and custom fonts, insert and format images, and add, create and changes colors.
A content management system is software that helps you build a website by using pre made templates. It often works as a user friendly WYSWYG editor similar to using Microsoft Word. This process can definitely be much quicker than coding by hand, due to using prebuilt themes. It also does not require the extensive education and knowledge of coding. A CMS is especially useful when creating a large website with multiple pages.
I think the main impact CMSs have had on the web design industry is that anyone can create and design a website. A definite drawback would be that you are using premade template that may not stand out as uniquely as a personally designed HTML website. I do not really think CMS are necessarily taking away web design jobs. People will always seek out personal professionals. Some people want the personal connection of working with a designer. Also the CMS must be constantly hiring designers to create the premade templates and keep up with industry evolution.
CMS vs HTML: Why Use a Content Management System? (coredna.com)