To answer some questions :
1. Why built an earth wall if it's weak against lightning?
It was meant to slow down the Raikage, a big earth wall can slow down lightning, but it can't stop it.
2.How can a full powered Kyubi mode Wind element Rasen Shuriken has no effect on the inferior Lightning element? Unless if there are still a lot of clones out there.
It had effect on Raikage, but he, with Edo Tensei mode, don't loose any health and was good to go again, so they(Naruto) had to do an attack that would damage the Raikage premanently. OR because his lightning armour is OP like Susanoo.
3. If there are still clones then what is special about Muu who has advance bloodline limit to be beaten by a fraction of Kyubi mode power?
It wasn't a clone, it was the real Naruto that beated Muu ... if it was a clone, why wouldn't real Naruto be with Bee? And he was beated because Naruto used his brain.
4. Even Hachibi's TBB only manage to deplete 3rd Raikage stamina, get real, how could he get killed by a wind user?
No where it says that he was killed by a wind user. It's said that he was killed fighting 10,000 mans 3 days and 3 nights non-stop.
5. And now Sage mode is faster than Kyubi mode, really?
Has someone said previsouly, it isn't fast, and as the chapter said, it was to help Naruto sense the danger of that jutsu and be able to avoid it.