What do you think

As the guy above states, Daki is the only reason why Gyutaro was even willing to become a demon. Daki got turned in order to save her life after being burned to crisp and Gyutaro in order to keep protecting her.

But if you're wondering, I'd say he would easily reach U5 and maybe potentially U4.
Top 3 are on whole different level and the gap between U3 and U4 is huge, so Gyutaro would probably never reach it.

He would still be Upper 6, despite what a lot of people want to think. Having Daki is in advantage for the simple fact someone needs to behead two demons at once. He is still far stronger than Enmu so if he loses Daki, he will remain Upper 6

Answer above is right.. but if you’re curious
Let’s say Gyutaro had access to Daki’s powers, combining both their strengths (Gyutaro’s endurance with his blood sickles along with Daki’s demon art plus her regeneration) would probably put them on par with Akaza or slightly lower. He would atleast pass Hantengu, Upper moon 4