next gens will always improve, especially in a young sport that is constantly evolving
but it doesn't necessarily mean they will be better than those who cross over from other martial arts.
these young people who train mma from the get go are referred to as "new breeds." there are already tons of these new breeds currently active but some are successful at the highest level and some are not.
it depends on the athlete. in a lot of ways it's better for someone to have a strong background in one martial arts, then transition to mixed martial arts and learn other aspects of mma to keep the fight where they have the advantage. and someone who trains in mixed martial arts right away can be good at everything but end up not being great at anything.
but it all depends on the individual. talent, determination and dedication,.........all ingredients to be a good fighter no matter what their background