It depends what your comparing it to. You don't need unreal engine, but if your going to add 3d then at least add collisions and 3d ray casting to finish the feature set. One of my biggest gripes with C3 is that a lot of things get added but never completed. Its just enough to entice you with what could be possible, but ultimately leaves you frustrated with its limitations.
To be fair, I think the 3d in c3 isn't meant to be true 3d. Its all smoke and mirrors on what are essentially 2d games.
I would agree with that what you say in a way, and I think that is my point. We still don't have a proper set of tools for 2d collisions and rays or a way to traverse object hierarchies. Adding in anything for 3d before even finishing this in 2d seems backwards.
Consider that currently there are no collision resolution functions except PushFromSolid (requiring a behavior to use, and solid tag on objects). This is very restrictive given the way c3 families and behaviors work. Raycasting is similar. Box2d provides an impressive array of tools, but most are not available when using that behavior (requiring additionally using c3 overlaps).
In my mind, given physics engine code is opensource, accessible, and to be found in great variety, I think c3 could easily offer more than it does in this realm, natively. Collisions are really core functionality (as are vectors), and c3 might be the only game engine I have used that won't provide the latter, and has a very simple simple solution for the former.
This is all okay if you are making retro style platformers (even then there are some missing tools for that), because the functions are lightweight and can be handled in events.... but, 3d?
Currently in 2d, we have no way of defining collision objects except by adding in objects with all sorts of extras we don't need. We have no way of creating compound colliders except by means of creating multiple sports or iterating through a sprites animation frames (bad for performance just to get a polygon). This is going to be compounded in 3d. We have no way of testing overlaping shapes and returning the points of contact etc... Box2d comes with a full sweet of tools, but many are not officially exposed. C3 doesn't have a model for detecting continuous collisions. C3 doesn't have swept shapes (which can be built off continous collision solvers). This list of issues is largely only solvable by rolling out your own code, but then you have the unpleasant issue with the fact you can't extend the editor.
All this applies to 3d. You need everything I just listed, or you are going to have the most basic problems of getting a fully 3d character controller up and running. You need to know surface angles at point of collision, and so on.