Competition would be great and need more support at the local levels. However it would take a very long time for others to catch up, if ever. The NRA took 150 years to get to where they are now. There's also a lot of other areas that the other national orgs don't do, or are extremely limited like lobbying congress, training law enforcement, youth programs, hunting programs, promoting guns to the general public.
Another problem is competition is sometimes a bad thing when you can't build unity. Lots of orgs and shooting disciplines don't like each other, but usually NRA serves as a unifying force.