As I always say, if you are near a music store that sells your keyboard and can conveniently get there, check out similar settings on their display keyboard to see if it sounds the same as your keyboard. If it sounds the same, then your keyboard is likely not defective.
On my older PSR-E433, I usually only use the styles for the drums, but I have not noticed them to be particularly loud compared to the main "panel voices." But with my "XGLite" voices, many of them have very low default volume settings, and they need to be boosted (using the main, dual, or split volume level settings, depending on which zone you're using for the voice) to be useable and heard over the style and other voices. But I thought they fixed this with later versions of the keyboard, like the E453 and E463.
I know the style volume level is remembered on my E433 after I turn the power off, and it does not have to be saved to a registration. So, if you find the style is overpowering many of your voices, just lower the style volume level. I suspect that the song and groove volume levels are also memorized after power off, but I haven't checked that on my keyboard.
Normally, I create custom "patches", or combinations of voices and settings, to get the sound I want, including the volume levels that I want, and I just save them to a registration -- but I save them to a registration WITHOUT a style. This way, I can set the style volume independently, and then when playing a song, I can choose a particular style and tempo for that song, and then use the registrations to easily change the sounds I am using throughout the song (such as using different sounds for verses and choruses) without changing the style.