The protagonist always 10 steps behind the enemy, always struggling and in shambles. It's so freakin trash story.
To be fair, Isaza and Saku did live sheltered lives. Not like their parents were assassinated or anything. Both of them are slowly becoming aware of their surroundings, and Hiwatsu at large.
Give Isaza some time, he just recently learned the pleasures of
murder combat.
This fight revealed to him, and readers what humans with stone powers can potentially accomplish. Isaza is still learning how to use his powers. Even in JoJo it takes Stand Users a (long) while to fully learn, develop/evolve, and understand their Stand’s powers as well as their limits and weaknesses.