Well... as I remember he does learns things more faster as he is sukunas vessel, especially when it comes to CT and other complicated stuff mentioned in the manga. It was not just black flashes he does learn some more few things throughout the arc. Yes it does feel like it's an poor story telling but in my opinion we get to see yuji growing more and more with or without sukuna. Yuji is the MC for a reason just overshadowed by other characters. Let me be honest, without yuji in the story it would be kinda boring if the manga it just about gojo and his dead BFF geto (aka kenjaku) epically with sukuna here too he adds more "excitement"??? (Idk) to the manga but I agree on what u are trying to say epically when generate is just killing characters left and right.
*gege
Thank you for saying it
He is the main character, sure. But this manga has poorest story telling ever. How did he get his power ups so far? We know nothing. What's happening during battle? We know nothing except some scenes from shitty flashbacks. Do we need help? Someone fell from the sky without any explanation of situation. I'm sick of this shit. Really. Wanna know how it's gonna end so I'm still reading but this story doesn't deserve its fame. Without MAPPA's work and awesome first season animation, without animated Gojo's visual impact, this poor writed fcked up story would never be here today.