Totally forgot about Rock Lee, Neji and TenTen being older and not being in the ninja academy class with him. You're definitely right. Nonetheless, he still knows about Shikamaru and Lee to an extent.Actually, he wasn't in the academy with Neji, Lee, or Tenten as they are a year older than him. He hasn't even seen Neji or Lee fight in the chuunin exams so he pretty much has no idea what they are capable of. Granted he did have a slight skirmish with Lee, but it was still nowhere near what he was truly capable of.
During the prelims in the chunin exams, he was the first one picked and had to leave straight after his match, meaning he didn't see what the rest could do at all. Then he was super late to the finals and only got to see gaara's abilities because of it. The only people he has a certain amount of info on is saukura, naruto, and sai to a little extent .
Even if they can't get through a full powered susanoo, there are other ways they can get around it. He is still vulnerable to attacks from below and shikamaru's and ino's jutsu can through it without any problem at all. By the way, the bugs don't have any chakra, so he can't sense them. That's why they have to feed off of shino's chakra to live.
If they all attacked together from different angles, he will not be able to respond against every single person as he only has a limited area of attack. Again hes's not just sitting there doing nothing-he is attaking them, but there is too many shinobi for him to counter at once.
I highly doubt Ino will be able to take over Sasuke with the Sharingan activated. And that shadow technique would require Shika to get in range depending on where they are. If they are in a very sunny area then Shika is done for, but Shika would probably have a chance to get to Sasuke at night. Still wouldn't be able to take down Susanoo, but its a start I guess. It all depends on the environment to me. If the OP would've given a location and a setting we would be able to put this thread to rest.
And lastly, he doesn't really have to counter them, Susanoo is a 360 degree defense so basically he could take them down one by one if he wanted to. He doesn't really have to look in the direction that he's defending... and Shino's bugs eat chakra, but they can't handle Blaze Release, so they prolly won't get through Susanoo at all...