well...if gai did this from the beginning, maybe before madara went juudara, or maybe when juubito was fighting, or maybe before obito went into juubito, or maybe ... u see what im saying. he should have just done this a long time ago, could have saved the whole world waaay faster. he should have been like "i need to stop obito from becoming the sage so i can save the world, save the youth!" his 1 life for everyone else would have been worth it especially when he was fighting the tailed beasts and obito, he could have handled all the beasts and obito or just go straight to obito and fk him up. i dont think obito could react to gais speed.