ok - i’ve found out that synfig won’t tween raster images - cool with that.
if i use something like inkscape to “convert” from raster to svg - and set the images up as keyframes - will synfig then tween the keyframes?
Tweening between completely independent vector images automatically is not supported. I don’t know if any software in existence supports that, it’s unlikely as doing it automatically would require really complex analisis.
What you can do is create the “keyframes” using Synfigstudio via editting in Animate mode. Yes, you can create the original shapes in Inkscape and import them if that works better for you, but from that point on the animation needs to be created in Synfigstudio (by doing edits at different points in time).
XD Elastic Reality. But it isn’t really a full fledged animation tool.
But like Yoyobuae says, if the world doesn’t work for you, YOU make it work, taking strides off the Tower of Babel and pierce the heavens! 
You just need to know what the tool’s used for first. LOL