Naruto also fought Pain alone, but Sasuke helped him against Madara.Sorry but it does not make sense, because Ichigo fight Aizen alone and defeated him. Why should he fight in his final act. with Uruuy how betrayed him. ??
Yhwach is Quincy king and Uryuu is Prinz von Licht, Ichigo is main character, deuteragonist betray antagonist and fight against him, I don't see why that don't make sense.
I could see Ichigo fighting Yhwach by the end alone, but I don't see why Uryuu + Ichigo combo don't have sense?