"True 3D" in Motion involves text only. But, "text" is a rather loose term. Any glyph in any font can be considered text and there are considerable resources to use to create 3D effects/objects in Motion. If you think about it, most 3D uses rather simple base shapes like circles/ovals and squares/rectangles. The real limitation to 3D in Motion is that shapes cannot be "revolved", only extruded (with numerous edge treatments like rounded, beveled, etc...)
Here's a playlist of demo videos for what can be done in "true 3D" in Motion:
https://www.youtube.com/playlist?list=PLjOCgGxNnAk4W3gTBk71qNsi8Yj2KULoh
The first 21 are Motion only. The rest involve mObject which is a worthwhile plugin to get for Motion from http://MotionVFX.com. You can import OBJ files into mObject (and the helicopters, cars and other complex objects all of which were free and available on sites like turbosquid.com.) mObject comes with many default 3D objects to get you started. [ There are at least two demo videos with links to free shape fonts for use in Motion/FCPX in this playlist. If you go through my regular FCPX effects, there are several 3D models available that also have fonts that accompany those models for their use (e.g., the Les Paul Guitar model).]
Considering the cost of software and the kinds of 3D that can be accomplished and the overall ease of use compared to other 3D software, Motion is rather awesome. BTW, any SVG file can be converted to a font at various sites on the internet (I use http://icomoon.io/app, but there are others.) If you know how to create fonts and already have the software, then I'd recommend staying with your font software. Since all the animation of 3D objects is exactly the same an any other kind of animation in Motion, creating complex animations is really simple if you're already familiar with the process.