Adobe After effects is totally layer-based software. It can able to do compositing, creating motion graphics, typography, and video editing, etc. Whereas Blackmagic Fusion is totally node-based software same as a nuke. But it’s able to make advanced compositing when compare with after effects. Fusion is mainly used for composting, paint, rotoscoping, and even the latest Fusion have a lot of features like making Virtual reality videos (VR)
Still, both Adobe After Effects and Blackmagic Fusion are post-production software. It will mainly focus on video, image compositing, and motion graphics, you can 80 to 90 % of everything in after effects and Blackmagic fusion. But when coming to 3D compositing Blackmagic Fusion is better when compared with After effects,
while in After effects, there are more options for creating motion graphics and animation components
For VFX, Fusion is the software that is used in a number of Hollywood movies been for over 3 decades. Fusion is free software in terms of some features and for some features, we have o purchase the license.
In Fusion 16 you will find various Keying options, that support 3d models which have been created in Maya,3ds max, blender, and other 3d modeling platforms, that come with the best planar tracking option and also has VR film making tools.
If you want to know about Maya and Blender. Please check out my recent article Maya vs Blender