I'm not sure why people are complaining about it being Ichigo at all. Lets be completely honest here, of all the people who are good if to be joining this battle which of them could actually stand on par with Ichigo, Rukia, Kenpachi, Byakuya, or Renji? Oh that's right none of them. And if these are the only people who have actually been able to make a difference in this fight for the most part how is someone who can't even stay on par with them or present a decent challenge going to fight the sternritters?
Grimjow couldn't beat Ichigo and we all saw what happened to Ichigo before his new power up. He got the crapped kicked out of him, and broke his bankai. His only saving grace being he was also of Quincy blood.
If one of the full bringers came back maybe the dude who could change peoples memories (forgot his name) might stand a chance. Might. Outside of that the rest are screwed.
I highly doubt Chad is on par with anyone of them either. He's like the Omeada of Ichigos group. Not to insult Chad. I like his character a lot. I'm just speaking objectively and used the best comparison I could.
Orihimes only use is her healing abilities so she couldn't have helped in battle.
Uruhara would actually be a challenge though. I could see him posing a real threat.
So there you have the squad of b list and c list characters who could never turn the tide of the battle. And even Kubo knows that. Their biggest contribution will be defeating the sternritters henchmen. Thus leaving Ichigo as the only person who could save Kenpachi and prevent total annihilation of the Soul Society.