Question: is issei stronger than sirzechs?
Answer: Divide can be spammed at about two per second, and gives the taken power to the user, this means that after two divides Issei (assuming he starts weaker than an infant) would be thrice as powerful as Sirzechs. Then Boosto, 3 boosts (about a second) would put Issei to 24 times Sirzechs power.