If you need to build simple (but not so simple as basic shapes) rigged models, my advice is to look into DUST3D:
Ui is not exactly optimal but, for the rest, you can build pretty fast.
I would actually be really interested to hear about this. I feel like there's a million new 3d packages out there geared towards simplicity and I'm still fumbling around complaining about blender.
I haven't messed with any animation but I've found Dust3d to be SUPER efficient for cranking out static meshes of various item objects for slightly higher fidelity prototyping.
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Looks like they'd be pretty easy to make with Blender's skin modifier, or might be a good candidate for dust3d. But as the other poster said, you could do it in any 3d software. It just comes down to what you're familiar with.
Dust3D is a pretty simple modeling tool with a unique workflow. It's more geared toward making organic models, so maybe not the best choice for a catapult, but it's something to be aware of.
Otherwise, spending the time to learn Blender like others have suggested is pretty invaluable if you can afford the time to.
I'm a solo dev leaning very hard on the development side rather than artistic, and I'm working on a low-poly flat-shaded game. It's a nice look, but it comes with much of the same workload as any other mesh-based 3D art style (i.e. you're still dealing with meshes and vertex shaders, though necessarily with textures).
Having said that, creating models in a low-poly style is often quite forgiving because the end product is, in some ways, an inherently low-detail model -- and while that may sound welcoming as a solo dev, just keep in mind that if you don't devote plenty of time to both A) creating those models in an intentionally consistent style, and B) presenting those models (e.g. animation, lighting) in an equally consistent and unique way, the result will look like every other solo-dev low-poly game that's been produced. This may not kill your game, but it most definitely won't stand out.
There's a massive amount of low-poly models and tutorials (serously: even just search this sub), so the opportunity is very real -- but you'll find very few high-quality low-poly games on desktop or console. They're well-suited for computationally-restricted gaming devices, like phones, and again, suffer from the "low-hanging fruit" issue I mentioned before.
I suppose the same argument could be made about pixel art, but in my experience (as both dev and player) it's easier to differentiate your work in pixel art than it is in low-poly.
I see those points as a challenge, so I'm writing mine for the desktop -- and I've spent the last several months just working on lighting, cameras, and shaders so that it (hopefully) stands out from all the rest. Voxel art is the style I really want to be working in, but I need to spend more time working with octrees etc. before starting on a voxel game.
You might be interested in Dust3D; it was made by a redditor who's shared the project's progress a few times in this sub.