what about people reporting that its not really 300mm on the long end so not providing much benefit over the 70-200 from canon anyway?
It is an industry standard practice to round the values. Canon do it too.
In theory, the front aperture should be 300/2.8=107mm in size. I just put a tape measure across the unobstructed front element of mine. It's near enough 100mm diameter. Therefore either the focal length is a bit less, and/or the focal ratio is a bit slower. It could be either 300mm f/3, or 280mm f/2.8, or somewhere in between. Regardless, it's still a truck load more than 200mm f/2.8.
What's more, the maximum focal length is probably a function of focusing distance. For example (I'm just inventing numbers here, don't quote me on this) the lens could be 280 mm at infinity, 240 mm at headshot distance, and less than 200 mm at closest focusing distance.
Edit to add: a quick bit of googling suggests 296 mm maximum (Amateur Photographer mag. review), dropping off pretty quickly to 260 mm when shooting test targets.