A 450 has more than enough power to haul you and your gear up any mountain pass. I've had my 250 up to 85mph, still pulling, just ran out of gear. Now, the question is, do you want to do that? Obviously not. You're not going to get a girl on the back of any race bike. These are totally different requirements.
KTM has a monopoly on the big race bike market because there really is only room for one manufacturer. For most people racing, a 450 is more than enough. The 500+ enduro bikes are for wide open spaces, and that market is very limited. The only guys I know up here with 500+ enduros have them just as a novelty, mostly because they couldn't decide between a real competition machine and a real adventure bike. So they get a race bike with a small tank and narrow seat so range is limited, big engine for more power in the wide open spaces, but is too heavy for serious single track use. You know, jack of all trades, master of none.
That market is very small. Most people are either going to race on MX tracks or small (10-100 acres) of forest which means 250's and 450's, or they want a bike they can ride 1000's of miles which means a real adventure bike. Not that many people in the world have access to 1000's of mile of desert to race in.
The Dakar needs more than one manufacturer to be a success.
Maybe what they should have done is made two classes, a 450 and unlimited. Stating both will share equal coverage, and it would have given the Japanese companies a place to race their smaller bikes that will have a return on investment (exposure).