Fighting isn't the only element of self defence but its a part of it. MMA is one of the sporting arenas that cultivate optimum fighting ability and the rest of self defence relies on other skills. The point is to consider your training's utility in other combat sports which utilise more permissive rulesets as a part of assessing how well your particular skills translate into a real fight. If you care about being able to fight. People who train JKD functionaly (for fighting functionality) will be able to compete in MMA or Kickboxing or open grappling events irrespective of whether they train for that arena specifically. If you cultivate the practical ability then you simply adabt for the given context be that sport fighting or self defence.