Kickboxing vs MMA striking
The techniques look similar and the stances are not. Everything a kickboxer does well becomes dangerous the moment a takedown is legal.
Kickboxing striking does not transfer directly into mixed martial arts, and the reason is stance rather than technique.
A kickboxer stands relatively square and upright with weight distributed for kicking and rotation. That stance is optimal when the only threats are strikes, and catastrophic when a double-leg is legal — square hips and an available lead leg are exactly what a wrestler wants. MMA strikers therefore fight from a longer, more bladed stance with weight back, which costs kicking power and rotational range but makes level changes defensible.
Gloves change the maths again. Four-ounce MMA gloves are smaller, which makes head kicks and punches land more cleanly, makes catching or blocking with the hands less effective, and shortens fights. A high guard that works in ten-ounce gloves does not cover the same area in four.
Some things survive the transfer well. The low kick is devastating in MMA and under-used, though it carries takedown risk. Long-range striking and distance control transfer. Clinch knees transfer. What does not is the willingness to plant and exchange in the pocket, which in MMA is an invitation to be taken down.
Fighters have moved both ways. Alistair Overeem and Mirko Cro Cop came from kickboxing with real success; several MMA fighters have gone the other way with less. The general observation is that kickboxing skill is a large advantage in MMA once takedown defence exists, and close to a liability before that.