I’m using the permalink structure /blog/%postname%/ for any reason when I create a single-posttypename.php the single page of this custom post type endup being like a single.php (getting body class single/ Breadcrumbs displaying the blog breadcrumbs)
This is not really in Types territory. Types tells WordPress that there’s a new post type and WordPress sets up the paths.
The permalink structure that you’ve selected seems a little problematic to me. In your place, I’d put the entire site in the ‘blog’ folder using the Apache Alias directive and use a simple %postname% URL structure.