If you really can build the exact same site, then why not use the CMS? The barrier to entry is great, but even just putting in (and filling with original content, etc...) your own CMS on your host does present a barrier to entry (it's not as easy as paying $100 to join a MLM or $8.00 for some VistaPrint business cards, for example).
That being said, if you really can duplicate a site that easily, try to figure out why more people aren't doing it. Is there a need for another site like that? Can you do something even better than what they are already doing? If tons of people are already doing it, you'll have to be even more exceptional than them in order to rise above the noise. There is a TON of noise out there.
On the flip side... can you build your own site? If you can and you think you can do it even better and more customized than the CMS option would allow you, then go for it!
Some action is better than no action