For non-technical users, you must use Plesk. Want to use WHM because cpanel is more familiar? Won't support the server at all.
Want to use CloudLinux because it makes multiple PHP versions easier for the less technical? Won't support your server at all.
So it's only fanatical support for a subset of what most vendors usually support.
Don't get me wrong, support is better than what you get with say eUKhost but a lot of stuff is faster to just do myself than pick up the phone and listen to some bad techno until I get through to Linux support.
Rackspace makes that clear from the beginning. Do you want someone who can support the most common usecases very well, Apache, Nginx, MySQL, Ubuntu, CentOS. Or do you want mediocre support that can support YOUR use case.
What you need is a consultant or a service that specializes in your particual use case.
As a former support racker I can tell you that while those might have fall outside our offical spheres of support you would have had no issues getting support for cPanel or WHM. CloudLinux support is a different story.
Kinda a kick in the teeth when you pay through the nose for an archaic machine because "we sell support".