For certain, there are disadvantages in any rules bound competition sparring format. Get too entrenched and you will revert back to the rules in a real-world self-defense situation.The way you are being taught in Kyokushin may be the best for that style approach or competition rules. Kyokushin training has advantages (e.g., prevent CTE, speed, etc.) but may also have disadvantages.
Some other poster, "There are a few others things that are very valuable in a street fight that kyokushin (at least in most dojos) does not teach you: One point kyokushin is often criticized for is the lack of punches to the head. They are part of the curriculum, but since they are not allowed in competitions, you don’t train them much. And while you don’t necessarily need them as an offensive tool (punching to the head bare knuckled is a terrible idea anyway), you sure as hell need to be able to defend against them in a street fight.
Another major thing that is missing is take-downs and ground game. Again, even if you don’t want to take the fight to the ground yourself, your opponent might want to and you better at least know how to defend that and how to get back up."
Where there are no rules.