It's all about using raw to manipulate the the exposure curve. You can get the same end result with an 8 bit camera, but the set lighting has to be perfect.
Simply untrue. First of all, everything isn't on a set. This argument holds no weight for location photography, particularly exteriors.
Secondly, on any set in which practical light sources play a significant factor, they will blow out to a greater or lesser extent on cameras with more or less DR. But you want your subjects lit so they are not underexposed. It's a tricky balance. And your light will be shaped differently if you use lights off-frame (not always a possibility, either) to fix your exposure so you can't just do that.
There are reasons that "digital cinema" came to prominence much later than dSLRs did and why only the Alexa (with dual gain paths) has really proved a viable replacement. Highlight headroom is crucial with motion picture film, much more so than with still cameras (for which you can use strobes and dodge and burn or shoot multiple exposures more easily or just wait for the right light, whereas films must be shot fast).
Yours is a bold statement to make. Either somewhat ignorant or extremely hubristic, imo.
That said, the 5D has enough DR for most work. Just because it's only very good for very cheap doesn't mean everyone's entitled to great for just a little more. The BMCC might be great with DR, but sensor size, usability in post and on set, etc. is terrible from the perspective of anyone except the hobbiest who shoots test charts or the small production company that runs a very small, tight ship and only really does one style of work (studio short form).
The Alexa blows them all away and you can shoot on it as you would shoot on film and it's an affordable rental. So thankfully there's that.