Looks like this change was introduced with EMR 5.22.0 release: https://docs.aws.amazon.com/emr/latest/ReleaseGuide/emr-5220-release.html
With EMR Serverless should be back to default 0.10 (10%): https://docs.aws.amazon.com/emr/latest/EMR-Serverless-UserGuide/jobs-spark.html#spark-defaults