Ukulele strings are bright, is my conclusion. Sure, wounds have more heft, but they're still hard, and so have a lot of attack.
GHS and Hilo sound a little mellower to me in some situations. I rejected them because they aren't as clear, but it might help a little bit.
Spruce on Rosewood is a very bright combo.
Spruce is light and vibrates easily, and rosewood is hard, so the high frequency spruce noise just bounces right off it, creating very hard sounds, and crisp crackly highs.
Might just not be your cup of tea. Someone else might love it though, so if you did part ways with it, it might be more appreciated elsewhere.
If I were given this task, and had to make it work, I would probably go at it from the physics side:
The rosewood is hard, so I'd spray something inside on the back that was softer than rosewood, like dilute tru-oil.
That would take the hard edges off the sound.
Then, I'd try to add weight to the soundboard to make it vibrate at lower frequencies, like a heavier bridge, saddle, or even something as simple as it sounds, attaching coins to the inside of the soundboard below where the bridge is. I'd first just tape them, and then if I liked the sound, I'd glue them.
That of course is in most people's minds heretical, but like I said, if I had to make it work, I would.