There is no one perfect brownie - there are good cakey ones, good chewy ones, good fudgey ones.
A good cakey brownie does NOT have the texture of cake. There's a big difference. The chocolate-to-cake-ingredients is different - more chocolate, but still has that lighter, layered thing happening. Mmmm. The right intense chocolate, the right amount of light pastry, perfection.
The contrast between the chocolate and the light texture makes a cakey brownie a good way to use a winy, delicious artisanal chocolate. Fantastic complexity. Or, a brownie that comes close to the taste and texture of chocolate mousse, but it's cake, is an awesome thing.
A good chewy brownie is a different animal entirely. In a cakey brownie, you want a rich chocolate to play off a light texture. In a chewy brownie, you need a chocolate strong enough to stand up to a heavier texture. It's a totally different balance. You would generally want it sweeter, and it can stand up to a lot of ingredient additives, from nuts and caramel or peanut butter to fruits, spices, all sorts of odd things. The opportunity for experimentation makes this brownie a fun thing.
The perfect chewy brownie texture is somewhere between the slightly-undercooked that a lot of people like, and an overdone custardy pumpkin-pie thing that a lot of bakeries call "chewy". While a perfect cakey brownie is a specific thing, a good chewy brownie has a lot of leeway. Still, the perfect chewy brownie is worth achieving.
The fudgy brownie can be wonderful. However, it is often the mistaken result of trying too hard to an extra-chocolatey chewy brownie. A brownie recipe can take a lot of chocolate, but experimenting will throw off the proportions and you will end up with some strange (often wonderful, but . . .) results.
Cakey brownies need a rich but delicate frosting, if frosting is added. The denser structure of the chewy brownie needs a frosting that is fudgier. Fudge brownies work well with a DENSE chocolate mousse icing - it needs to stand up to the brownie, but a contrast is the goal.
Also, the size of the finished brownie is a concern. A big slab of brownie needs a strong structure in order to not fall apart - but too often structure comes at the cost of good chocolate. A smaller fudgy brownie, if perfect, is a work of art and a wonder - but people, being human, want BIG PIECES.
The thickness of the brownie is also of note. Each set of ingredients has an ideal height that will best marry the goodness of the ingredients, the heat of the oven, the forming of the chemical lattice that will make the best product. As always, much testing is needed.
Well, you DID say discuss . . .
Edit: of course we are talking about CHOCOLATE brownies. There are things called "brownies" that don't have chocolate in them. Abominations.