Why wasn't this given an upcast for more targets? You seem to have added upcast to most other spells that could logically have one.

Because 3/4ths of the party have natural darkvision

How in the world is this not divination or enchantment. In what world is this transmutation!?

Quote from lalalarix1 >>

How in the world is this not divination or enchantment. In what world is this transmutation!?

Divination spells are largely about either seeing the future, contacting extraplanar entities, or seeing what's going on in a place far away from you. Enchantment spells are mostly about manipulating other creatures' emotions. Neither of those things really apply to this.

Transmutation, though, is about changing a creature or object's physical properties. Spells like this one (and, e.g., Alter Self) that alter a creature's senses or capabilities fit that definition.

Darkvision is common enough for both PC's & NPC's that darkness rarely has a mechanical effect in combat, unless the DM goes out if their way to make it one. Someone with a greater range to their darkvision could potentially abuse that against a creature with shorter range tho, and 150 feet makes 90% of creatures fair game for that strategy if you're a long ranged character.