Czar already confirmed in a 2K19 video on YouTube that ACE is set to run around 60% of plays out of a team's Series/Freelance depending on the quarter. If you test this with Playcalling Messages ON and ACE ON, then this is easy to confirm. I'd estimate it's around 40% of the offense in an entire game being run through Series/Freelance and it does not depend on the Run Plays coaching slider at all. After that it's basic math to see the impact.
If you play on 12 min quarters, then teams are averaging around 100 possessions per game. Teams are making 45-50% of their shots and another 10% of possessions end at the free throw line or with a dead ball. That's 60% of the offense (or 60 plays per game) coming out of half court sets. If 40% of those half court sets (24 plays) are Series/Freelance as controlled by ACE, then that leaves 36 plays to be called out of the team's playbook.
Czar also stated in his video that the default ACE setting for most teams is to run plays for the #1/2 options on the floor. This is also easy to confirm as the Touches tendency does not spread play calls around the floor with ACE turned ON. On a team with established stars that doesn't use the bench a lot (i.e. not the Nets with 9 guys getting 20+ minutes), this means 3-5 players per game will get actual plays called for them out of those 36 set plays. There's not much variation in those plays, especially not if any of them are running Isolation plays. If the two lead players on the team are both similar players (think CP3/Harden, Lillard/McCollum) then they will typically alternate running the same plays but with different play initiators. There are only 4-8 plays per play type in most playbooks so it's going to get repetitive with only a couple of players deciding which plays get called. Substitution patterns matter too because mass subs will reduce the possible lineup combinations to bring new guys into lead scoring roles.
I'm seeing 10-12 different set plays called per game on 12 min quarters with ACE turned ON, up to 18-20 different set plays called if the team has a Series in their default config. With ACE turned OFF, I'm seeing over 25 different plays called each game and can still call Series during timeouts to bring that up to 30+.
In addition, the ACE system triggers the same exact sequence every single game. You can test this with the Rockets and they will run 21 Delay (used to be Point) for the first 6 minutes of every single game no matter what. They follow this with Harden/CP3 Isolation on default rosters (assigned play types in custom rosters) until the bench takes over and then switching back to 21 Delay and repeating this cycle until the game is over. The play calling itself is static for large chunks of the game with branching options on each play for passes/actions in Freelance.
Each team has 50 plays in the playbook and another 20+ plays/options added through Series/Freelance. There's no reason we should be seeing the same game script most games, but Czar probably hasn't pushed his updates to the roster yet and we're still playing a half-finished product.
I'm not posting this to talk down on the ACE system as a whole, just to say that the version that shipped doesn't seem to be game-ready yet and there's no ability to turn it OFF for the CPU. This feature should be the future of 2K's AI system so we need to have ways to give feedback that can be rolled into future versions or the ability to customize the config without having to hound Czar on social media.