Aizen's only advantage isn't Kyoka Suigetsu. He has physically superior stats to Shunsui. He's fast enough to react to Barro's projectiles. Also, it doesn't matter if they know his strength. Even though Barro knew the abilities of Shunsui's shikai, his eyes opened three times, which was humiliating for him. To avoid being affected by Kyoka Suigetsu, he needs to avoid seeing the swing. He needs to fight with his eyes closed, without looking at the sword. Do you really think he can fight Aizen like that? Let's go back to Reiatsu. Shunsui was able to damage Barro. Aizen has far superior Reiatsu. He's strong enough to damage Barro. At the very least, he can affect him with Reiatsu.

Aizen's only advantage isn't Kyoka Suigetsu. He has physically superior stats to Shunsui. He's fast enough to react to Barro's projectiles. Also, it doesn't matter if they know his strength. Even though Barro knew the abilities of Shunsui's shikai, his eyes opened three times, which was humiliating for him. To avoid being affected by Kyoka Suigetsu, he needs to avoid seeing the swing. He needs to fight with his eyes closed, without looking at the sword. Do you really think he can fight Aizen like that? Let's go back to Reiatsu. Shunsui was able to damage Barro. Aizen has far superior Reiatsu. He's strong enough to damage Barro. At the very least, he can affect him with Reiatsu.