Blender vs. Fusion

Not knowing much of anything about Blender -
Is it worth considering over Fusion/Resolve for comping 3D objects?
What does Fusion/Resolve do better?

Blender is a 3d app. It's for modeling, rendering, lighting, animating. It has some 2d compositing features, but that's not what it's designed to do.

Fusion 9 is a 2d compositing app. It's for color correction, integrating 3d renders into photographic footage, welding pieces of footage together so it looks like they were shot at the same time, finishing, optical effects, and so on. It has some 3d features, but that's not what it's designed for.

Resolve (now with 100% more Fusion) is an editing and color correction program. It's for creating a sequence to tell a story. It has Fusion bundled in, but it's still not as good at compositing as just using Fusion on its own.

Each piece of software is a different part of the full production pipeline, and you really need all them or their equivalets (plus a few more, probably) to get everything done. None of them can be completely replaced by any of the others, even though some overlap of functionality does exist.

blenders compositor is bascially designed to do basic compositions on the fly.
Feature wise its very basic compared to fusion...I have used it in the past for some compositing stuff and still use it for comping 3d render passes for preview while setting up a scene for rendering. (For example, unlike other 3d applications, you have to do fog in the compositor)
For thats the kind of stuff its perfect...but I still use AE or fusion for the final comp.

The _big_ problem with it beside limited functionality is speed. Its drastcially slower than any compositor out there and does not allow you to cache preview...so you need drastically more time in it.

....
Still like some of its nodes though: its lens distortion looks nice, also the channel key wich allows you not only to key out with rgb or hsv tolerances but also with YUV and YCC is an interesting concept.