Ahh, I see what you're talking about now, and you are correct. My graphics measured differently before and after importing so this must still be an issue with Fusion. But actually, that doesn't bother me at all since an SVG is meant to be scalable. I would never use an SVG for precise machining, but they are great for art projects like the OP's sign.
TomCat, this would be my workflow. If you plan to do multiple signs such as a business, I would create a project where I kept a sketch of the outside of the sign. The dimensions would be driven by parameters called length, width, border-offset and corner-radius. Then from Illustrator I would save the design as an SVG and import it into Fusion along with my sign border sketch:
Scale the SVG until you get the results that you like and do your extrudes until the depth looks the way you want it:
Then do your toolpaths. This is a simple 3D adaptive clearing but you get the idea. There are other 3D strategies to choose from that can be applied to different styles of geometry in your sign...you'd have to experiment a bit. This isn't perfect, but I think it's pretty close to the picture in the first post.
I'm not trying to make this a Fusion vs. Vcarve discussion, but since the title of this thread involved Fusion it caught my attention. I still want to get the demo of Vcarve to play with, but since I don't do signs it's kind of hard to justify the price. If I can finish my router table project, that may change :-)