> the momentum Java 8 gained when it was released in 2017, 8 years after Java 7

Java 8 was released in 2014, a little less than 3 years after Java 7:

Java SE 6: December 11, 2006

Java SE 7: July 28, 2011

Java SE 8: March 18, 2014

Java SE 9: September 21, 2017

Java SE 10: March 20, 2018