"Breaking in" headphones is a myth. Your subjective listening preferences adjust to the headphones that you use. You may get a more comfortable fit as the band and cushions conform to your exact shape, but the performance of the drivers isn't going to change significantly.
I have been well-pleased with all of the Sennheiser headphones that I have purchased over the years, including the very well worn HD430 set that currently serves my PC gaming & music needs.
i7-8700K, H100i v2, RoG Strix Z370-G Gaming, 16 GiB, RX Vega64, Define Mini-C, SSR-850PX, C32HG70, RK-9000BR, MX518