May be
bcoz
# Similarities#
1. Sage of six path has Huge amount of chakra whereas Madara has Infinite Chakra(due to edo)
2. Both have well developed awakened(not borrowed) rinnegan
# Differences#
1. So6P Sealed juubi ,even breaks it into nine different tails, but Madara has difficulty in handling juubi ,mainly obito is handling juubi
2. Madara has both uchiha and senju cells but So6p is source from which uchiha and senju originates so he must be more powerful than Madara