Sorry but Sage Naruto fought on par with Pain. Also doesn't Naruto have extra clones that he can summon and on top of that an army of frogs. He also has Ma and Pa. We all know Lee is weak against genjutsu. Also if Lee in gates is untouchable, how come he got his legs injured by Gaara who has much slower reflexes than Naruto. Naruto is a tank and filled with a strong life force so I don't see how some punches and kicks from Lee will faze him. Also frog kata is one of the best forms of taijutsu and combined with Naruto's sensing, Lee has a lot of trouble on his hands.
Just because someone is incredibly fast does not make them invincible. Also remember sand armour tanked all of Lee's attacks. Sage Naruto will have an even lesser worry.
It also just so happens that team guy was away on a mission when pain attacked. Im pretty sure that it would have been different with 2 gates users and a talented hyuuga shinobi there to help.
Lee is untouchable when his gates are activated and he is moving around. Gaara crushed his legs after he had finished and was vulnerable. This isn't exactly regular taijustu were talking about here. Lees already incredible strength and speed are exponentially increased with each gates that is opened, at the cost of his health. The gates aren't classified as a kinjutsu for nothing.
Dont get me wrong, Sage mode is definitely more versatile and would be the more likely choice to use against any opponent. The gates are specificly used as a last resort when the user is not able to defeat his opponent in his base form to allow him to temporarily overpower his opponent with phenominal speed and strength.
I understand that speed/=invincibility, but it would be hard for Naruto to actually land a blow against someone who is several leagues faster than he is. The sand armor was destroyed by Lee in the 4th gate(he only opened the 5th for the finishing blow.) and the only reason why Gaara survived was because his sand gourd cushioned his fall from the the final blow.
