Hence the keyword: alive. Edo's are almost always weaker than the individual's alive self unless they had something during their life holding them back. (i.e. hiruzen and his age, itachi & kimimaro with their sicknesses, etc)
This is Madara after he comes back to life:
Just his vigor coming back to him from the Rinne Rebirth breaks through the Deity Gates, something that only Juubito's physical attacks and Tobirama's paper bombs could do. When he was an Edo, he was still trapped in the Gates.