i think yamato was getting stronger before he got captured. he used the first hokage's signature jutsu on the turtle island (vitality of the world of trees), made a wood rampart so aoba could walk on kurotsuchi's lava, kept kisame held down for a long time with his chakra supressing wood stocks. plus he has an arsenal of water and earth jutsus. over time i think he'd catch up to at least edo hashirama's showings. plus hes said to be one of the, if not best of anbu and personally selected by tsunade to guard naruto in all 4 missions. he also captured tobi at one point though i suppose tobi came to talk. and he had enough chakra to power up all the zetsus. hes versatile, no idiot, very experienced and great at tracking/gathering information.
