I am astounded by the number of pieces on the board by round 17! I only have two serious players in my gaming group (myself being one of them ofc), one player who is moderately into A&A and a few more who will play but view it as a simple board game and expect it to only go few hours and are unwilling to play more than one session.
As a result most of our games end at about round 6-8 when the weaker players quit due to lack of interest.
We have been fortunate to get a few games to go 15+ rounds. But every game we play we have very few pieces on the board compared to this because we are all very agressive players. Especially me and my friend who play axis. We are under the impression that if you don’t play agressive the game gets bogged down in stalemates and/or the axis lose out economically in a protracted arms race and a stragegic war of attrition.
So we never let a fleet or ground force get as big as you guys do which makes me guess that your group as a much slower and more cautious defensive style of play. Is that correct? Its the only way I can account for your giant forces.