Shinji went head to head with Aizen because he thought he could take him, he didn't account on the first encounter being interrupted by Kaname Tousen. Also Shunsui pulls off the idiot demeanor but is very smart (do I have to remind everyone him and Ukitake were the first to graduate the academy). Also Shunsui would know about Sakanade's powers because Shinji became a captain, got excommunicated as a captain and became a captain once again all during Shunsui's captain hood in the Gotei, so I am pretty sure he knows full well of Sakanade's powers and how to counter them.
Rookie, you obviously do not know who I am, I know full well what Zommari said to Byakuya, but Byakuya is not the fastest Shinigami but yet was faster than Zommari, also how would Zommari know how fast Starrk was? The top 4 were not allowed to release their Resurreccion inside of Los Noches. Also when we saw Starrk recapture Orohime, it was obvious that Starrk was the faster of Zommari and Starrk. Don't even try to bring the after image thing into play here, Starrk used it as well.
One Byakuya isn't the only one who is "smart" in combat, Starrk was able to tell Shunsui's dominant hand from his weaker one, then could tell how Shunsui was able to correct it mid battle. Also He figured out every aspect of Ukitake's shikai's ability in only three shots, first one caught him by surprise, second one was a theory shot, third one was the shot that allowed him to understand it. So ya Starrk is no slouch when it comes to perceptiveness in the middle of combat.
"Byakuya would not let that happen" The ****? Seriously he wouldn't let it happen, rookie I don't think Byakuya would have a choice in the matter. Shunsui was going to use Bankai against Starrk was was told not to use it where so many can see it. Also Shunsui's shikai only uses it's abilities when it wants to. Also never say there are no Shadows, shadows are everywhere even when they are fighting in the sky there will be shadows. He doesn't need to use shadows remember the color tag? remember the wind techniques? Byakuya isn't as skilled as he leads on, he uses his damn Bankai like a crutch, I mean seriously when have we seen him fight someone and Not use his bankai against that person? Oh and another thing on Senbonzakura not letting something happen to Byakuya......Renji vs Byakuya
To strong? Hell his Bankai doesn't even rank in nor near the top 5 for "strong" in Bankai's, they stole it because they knew it was one they could steal, not because they "feared" it. Hell Byakuya gave into fear when he couldn't use his precious Bankai in battle. Then I suppose I am a fool for believing him to be dead