I've been learning to use Freecad for a while and would never consider Fusion,given the way the providers move the goalposts regarding what capabilities they might allow access to.That being said,it isn't easy or intuitive too much of the time.I have zero experience of 3D printing or the software best suited for the purpose and may be a long way off the mark for suggesting that the Tech Draw workbench isn't really used for much more than producing old style 2d drawings.I would suggest the Part Design workbench is where you ought to be working as the constraints while sketching are the factors that govern a shape.I suppose the sectioning aspect of Tech Draw is useful for verifying that the characteristics of any given location are as desired.It might help with arcs if you delve into the options and switch the "show arc centres" selection to "true".It might need a recompute to update existing sections.