To start, I downloaded seasons 17 to 51 leaderboard data from https://mwomercs.com...le/leaderboards . Players are categorized into 5 Win-Loss-Ratio (WLR) brackets: 0.9-1.1 is Green, 1.1-1.3 Blue, >1.3 Black, 0.7-0.9 Orange, and <0.7 red. Each bracket contains roughly 20% of the monthly population, the exact pop % in each bracket is labelled for each month. To calculate monthly player retention, we check to see if each player appears in the next month's leaderboard. If yes, then the player is retained, if no, then the player is lost. The graph shows the % player retention from each bracket for each month.

What this graph clearly shows is that players in the green bracket are the happiest of the five brackets, consistently, no matter what patch release or turmoil is happening that month. On the other hand, the Red and Black brackets, the worst and best performing players, are consistently the least happy of the five brackets. If we could put all players into the Green WLR bracket, we would get to use the highest retention rate for the entire playerbase.
There is only one feature responsible for which bracket a player falls in: the Matchmaker. Take my word as a pro that does this for a living, that it is easily possible for a Matchmaker to put ALL PLAYERS into the Green WLR bracket. The fact it doesn't, as shown by this graph, means that 50 out of every 100 players that left this game has done so because of the Matchmaker. If from the beginning we had a Matchmaker that put all players into the Green bracket, we would have a 50k playerbase today instead of 15k!
Since 50 out of 100 players already leave due to the Matchmaker, it is hard for another single feature to be more important wouldn't it? Therefore, the Matchmaker is king.
Did I convince you? Leave your Yes/No and Why in a comment below!
Some extra discussion:
Is using leaderboard data accurate?
There are issues such as alt accounts and player name changes. If PGI wanted to do this graph using hardware ID rather than pilot name, it would be more accurate. However I don't expect the overall numbers to change too much.
Can the Matchmaker really be improved?
This image from https://mwomercs.com...psr-comparison/ shows that using a bad WLR Matchmaker would put 60% of the pop into the green bracket, instead of 25% with our current Matchmaker. Explaining a good Matchmaker would put all of you into a coma so I'll pass on that.

Tracking next month for retention is too little, what if the player comes back afterwards?
Here is a graph showing retention as if a player returns in the next 3 months. The numbers are higher as expected but there is no difference in the effect of the Matchmaker.

What other features are impactful?
I compiled them here https://mwomercs.com...war-escalation/
They are marked with a (!), the rest marked with (o) are just my preferences.
Edited by Nightbird, 19 November 2020 - 06:11 PM.