Neji isn't slow. Gai said the 5th gate WITH the Ura Renge was the key to beating Neji. He obviously can beat him if he tries any less. The stronger the attack on the user the more hurt the person who did the attack against the kaiten. Neji is quite fast as seen with his battle agasint kidoumoru. He also was easily beating all does clones of Naruto attacking 2 and a lot more at a time withotu even being tired 1 bit.

You can't base the power of each with characters. You can know what it's capable of but you can't say since Neji > Sasuke or Sasuke > Neji the sharingan/byukagan is better. We haven't seen any main family moves aside from 2. We've seen 2 of the strongest move for the sharingan.