It's the age-old question. Clearly, the PS/3 hardware is capable of better sound than they manage to produce for their steam locomotives.
The real mystery is the MTH and Legacy diesels both have high quality sounds as a rule, and you'd likely be hard pressed to tell which is which just listening to the sound. Why a vast majority of the MTH steam compares so poorly to Legacy befuddles me.
I will say that Lionel puts more though into the acoustics, even small steamers have a decent baffle to improve the sound. Many of the larger steam go with dual speakers for improved sound, especially the bass.
I have the MTH 2017 Catalog Premier Restoration Version Big Boy, not a cheap locomotive. The original sound file sounded like a wounded cow, there was no mistaking that for any train whistle! I loaded one of the later sound files and got an incremental improvement, but any one of my Legacy steamers still beats the pants off the sound quality of this locomotive.
I picked up the 2023 Legacy version and I'll be selling the MTH version...