https://emulation.gametechwiki.com/index.php/PlayStation_emulators
1. There are quite a few options besides Duckstation already.
2. Is there anything wrong with Duckstation?
3. I don't have a problem with yet another PSX emulator existing. The more hats in the ring the better. However, using an emulator with whatever imperfections it may have within another emulator that is far from perfect is about as impractical as you can get. Emulating the Vita is also far more resource-intensive than just emulating PSX. There simply is no reason to go about playing PSX games in such roundabout fashion.