US-based answer, and I'm not a doctor.
I don't know what "no night vision" actually means. But let's assume you mean someone has some kind of difficulty seeing clearly in low lighting conditions (again, whatever that means). You seem to be asking two questions here: is night vision important for pilots; and can someone with limited night vision get a medical?
At least theoretically, night vision only matters to pilots who fly at night. I know several pilots who have daytime-only restrictions on their medicals because of limited color vision. I assume (but don't know) that if someone had a hypothetical condition that meant they could see perfectly during the day but not at night, the medical examiner could issue the same limitation:
Not valid for night flying or color signal control.
You suggested that a pilot with poor night vision could just fly on instruments at night, but they have to get the aircraft to the runway first. And takeoff and landing both require visual cues, including seeing airport lighting at night. If the pilot really has difficulties seeing at night, it isn't obvious how they could safely operate an aircraft on the ground, never mind in the air.
As for a medical, I couldn't find anything in the FAA's medical standards about low light vision specifically, but there is some general wording that seems like it could apply:
Congenital or acquired conditions (whether acute or chronic), of
either eye or adnexa that may interfere with visual functions
I have no idea how a medical examiner would address any issues. They might have to defer the case to the FAA for review.