All combat damage is dealt at the same time, so yes, it would have been a draw.
Deflecting Palm is a sort of replacement effect (instead of your opponent, you take damage the moment combat damage is dealt). This happens at the same time for all combat damage. So, the Polukranos damage hits you the same time the Arbor Colossus damage would have hit your opponent.
Extra, could be related to your question. When you play a best of three match, and one of the players has won a game in that match, the match would've ended in a 2-1 score for the player who led 1-0. So if your opponent was 1-0 against you, he would've still won the match. The other way around if you were 1-0 in the match.