No, Madara is not as strong as the Juubi, he just happens to have a trump card, something he'd set up while he was yet alive, as a just in case thing.
Obito did not exactly absorb the Juubi He absorbed its chakra while simultaneously sealing it. It stated that he absorbed the Juubi's Chakra as per Hinata, while it also stated the he performed a seal to be the Jinchuuriki as per Naruto.
Don't forget that Madara and Obito are virtually clones of Hashirama, body wise.
People keep underestimating Obito's strength, even if he is not showy, or he is not first rate, Obito still has a body compatible with Hashirama's along with the privileges of Mokuton. Obito would still have become the Jinchuuriki even if the Juubi had been in it's final form, as long as he had the strength (from being an injured Hashirama Clone), to remain focused, and as long as the sealing Jutsu invented by the SO6P continued to work.
As for the SO6P, we just don't know enough about the battle yet. Maybe the Sage had several fights with the Juubi before he came up with the sealing jutsu, or maybe he had to fight to stay alive while he was thinking up the seal.