Hello there! How is your labor day weekend going? For me, I'm working all weekend (minus Saturday) as it is Move In day/weekend at the University. Anyhow, with that in mind I figured I'd talk a bit about FATE and how comparing FATE Core to Dresden shows you just how much you can do with the system, provided you're willing to put in the development work.
Fate Core as a book is about the size of a hard cover novel. Not a huge GRRM Game of Thrones novel, but just a regular about 300 page novel. Dresden Files on the other hand is significantly larger, coming in at the size we expect for a RPG core book with some extra thickness too boot. Now, to be fair to Dresden, we should also include the FATE System Toolkit for Fate Core, but that is another novel sized book of similar size while Dresden also has a second book (the Our World book) of the same length/width but a bit thinner in the page count.
The Core Differences
Now both books/systems have very similar sizes in page counts and you could argue about art and lore and font size, so ultimately we'll say both are about the same size. However, when you look at the Dresden Files you have a complete system intended to give you a very distinct world type in the Urban Fantasy Genre with a lot of stuff for that one world. Effectively, there's really only one way to play Dresden Files if you go by the book, and that is as an Urban Fantasy game involving specific groups already set up.
Fate Core on the other hand is a tool box. It doesn't care what kind of game you want to play, it has what you need for all of it. You want Urban Fantasy? Great, go for it. You want Mecha and Magic? Got that too. How about cyberpunk? Also covered. Or you could combine all of those into a Cyber Punk Urban Fantasy w/ Mecha and Magic. (ok....now I kind of want to run that....stupid brain...)
But What Does That Mean?
What it means is there is a different depth to the mechanics. Fate Core has a lot of mechanics that can work well because Fate is designed around simulating narrative rules, but the system doesn't go particularly in depth with anything. Dresden on the other hand picks and chooses the aspects of Fate that work for it, then goes really deep into them - developing new rules as it goes along and using standard tropes in different ways to represent things.
On top of that, Dresden focuses more on building a specific world, a specific feel, and a specific playstyle which can be seen everywhere from the presentation of materals to the bits of fluff that are used to explain it.
So if you wanted a deep, complex system like Dresden for something you did powered by Fate, how would you do it? First you need to understand how Fate works. You need to know how to handle "everything is an aspect or a character" and what that actually means. Second, you need to know how to make mechanics that fit in with how Fate works but keep up a steady flow. Third, you need to realize what tweeks were made to Dresden to bring about the way the system works.
For one thing, Dresden Files' supernatural abilities are effectively glorified stunts with higher refresh costs. So when you drop 2 refresh into increasing your strength it is effectively the same as buying a stunt for a "Might" skill only the game detaches it and gives you some extra bonuses and a new heading. Ultimately though the balance and power level is about the same, they're just not attached directly to a skill.
Magic, on the other hand, is a combination of a skill (whatever skill is associated with your magic of choice) one of those super stunt powers, and then a system built up to give it more flow and direction. Effectively Magic is 2/3 Fate and 1/3 new development.
Finally, you need to sell your world. This isn't system design though, this is story telling and fluff building to give the world depth, themes, and a compelling feel to make people want to play there. For ideas on how to do that look at other popular worlds and what they've done. RPGs are full of these, so you have plenty of examples and you can always steal ideas from other places and mix them into your own brew.
In The End
In the end though, the big point here is to show how much you can do with a well designed system that focuses on simple but flexible rules. FATE is fairly easy to understand system wise. You roll dice for a result of either +1, 0, or -1, and you spend poker chips (Fate points) to do special stuff. That is effectively the whole system, but how you use it and what you build around it is up to you.