Originally Posted by MrBIG
I don't know if it was pointed out in the manga or if it was in the anime instead, but Oro's Edo tensei at the time wasn't perfect and the first and second came back severely weakened compared to when they were alive.
That is actually a misconception. Tobirama did not claim that the previous edo summoning of him and his brother was not perfect. ONLY that Oro had perfected edo tensai, which was done before the first time they were revived against hiruzen, and thus brought them back at practically full power.
Therefore, the first time he and hashirama were brought back, they were just as strong because edo tensia was already perfected. I mean, how is Oro going to perfect eod tensai further with his jutsu in the shiki fuujin? Makes no sense.
SO they were always at practically full strength, just likely being held back by Oro because he was toying with hiruzen the whole time anyways.