Given that my only tool for this besides razors is one of those crappy saws, I'm keen on reading up on the rotarys. I think Ross used one for his veneer panels blog which seems to excel.
I can get good edges with a chopper type paper cutter. but the shearing action tends to crush the veneer slightly at the edge so even if the fit is tight, there will be a slight dip and the joint.
One success I've had was using two 1/2"x3" sections of aluminum bar stock to sammich the veneer pieces between. Then a sanding block to match and square the edges to the bars. Any form of cutter always has produced flakes or chips from grain issues and the odds of having "downhill" grain for using a plane are near 0.
Anyway, the obvious solution is to become one of these experts!
Practice and then practice some more.