Oda brought Kizaru into this arc to clearly highlight the difference between a Yonko, an Admiral, and a Gorosei. Kizaru needs to rest and is severely hampered by it, every time he receives an attack from Luffy, the Gorosei instantly recover and start attacking back.
At least in terms of endurance and thanks to their regeneration, the Gorosei stand out and withstand the attacks that Kizaru needs a break to rest and recover from the attacks without Adcoc.