its probably not a sealing jutsu, just one that took the kyuubi out of the fight making it so hashi could fight madara 1v1....also it isnt stronger than kurama as its just a jutsu, not a real dragon(like saying water dragon jutsu is stronger than a bijuu) it is simplay a way to restrain the bijuu by binding it, kinda like shikamarus shadow possesion jutsu...if one is powerful enough to break it they will, but he was able to bind even op people for a time....and those people were much stronger than him.
SO its simply a binding and nothing else