I've come across many developers who have been through the bootcamp process. Some were great, some less so.

The worst thing that bootcamps can do is to encourage developers to simply "pad" their GitHub accounts with exercises in order to have used as many technologies as possible. I've seen developers bragging solely about the number of repos and commits they have in GitHub.

Generally speaking though, some people come through the programs having gained an incredible amount of skill, some people were already very good and simply looked to extend their skills, and some came through without gaining much at all. Much like any education program.