I don’t agree about Fire signs not being intuitive. Intuition is immediate cognition without rational thought:
Who better than Fire to achieve the immediate?
I do agree about instinct and intuition being used interchangeably when they shouldn’t be. I often think that Water is credited with being intuitive while really being instinctive. They have gut level knowing and response- not direct perception. The exception, I think, is Pisces because of its connection with Neptune. Cancer and Scorpio seem to have strong instincts- they feel what they don’t know. Intuition has nothing to do with feelings.
Air seems the least intuitive, or instinctual, because they run everything through their minds first. They logically and rationally figure things out. The exception is Aquarius because of its connection to Uranus. Uranus connections speed up cognition processes and help a person to skip steps to reach understanding. Neptune connections blur boundaries and make the unknowable, knowable.
I didn’t mention Earth in my comment, but I think that Earth signs know things through simple common sense. They look around, they see what’s happening, and they draw realistic conclusions about underlying motivations and possible outcomes. However, a person who has a lot of Earth, or Air, planets with a well-placed Uranus or Neptune, would have stronger intuitive abilities than the average Earth/Air person.
I think that we all have gifts in understanding, I think that we all have psychic tendencies, but, I do think there is a difference between instinct and intuition (and common sense and rational judgment). Each element (Fire, Air, Water and Earth) has skills in cognition, and may reach the same conclusions, but the methods are different.