Those wee drivers haven’t been softened up yet. In production, the drivers are assembled, tested for resistance (connections), then operated briefly to see if they vibrate, and that’s about it. To run them for hours is asking for valuable production time.
Many, I’d say most, drivers will sound fine from the first hour. Others, especially the ones I happen to like, the iM490S Maximos_,_ sound like crap “out of the box”, then they bloom to a wonderful sound after a day’s operation, especially in their ability to reproduce a warm bass.
Hey, I’ve had plenty of expensive devices, but a daily thrasher like the Maximo or the JVC Air Cushions is wonderful. These devices are all $50 or less. I have three testers here (daughters) that are guaranteed to run ANY headphone through some outright torture.
Your SONY phones should benefit from a day or so of use. I’ve always been disappointed with Sony earbuds, as they sound more “tinny” to my ears, though the build quality is very good. After a day, your 'buds should sound better.