I'd say using a square as a reference and tracing the image is a proven method... Infact I thought it was pretty common knowledge. I learned it on here even! We were talking about getting a perfect contour on a vehicle for some police cars... Some people used chalk and kraft paper, some just kept modifying templates... Then someone mentioned a couple 12" magnets / squares... Take a photo, scale the image so the squares are square and you can get almost pinpoint accuracy. I went and cut some squares, took a photo... And it was dead on. Took me 5 mins and works for so many things.
It's not (in my opinion!) Re inventing the wheel... There's been tons of times we were doing vehicle wraps or PPF and the template was off and we didn't want to cut off n the vehicle... So we did the square method, without fail it's never let us down. On channel letters it may be acceptable to exact into the material, but plenty of other things it's not.. so being able to get a quick and dirty template with a photo is a good skill to have!
And let's face it, how many people on here has a steady enough hand to hand cut it, even using the letter as a guide? How many would be able to graphtec a 12" square, take a photo, blow it up and then use the pen tool to draw an outline?
Your ways cool, and being able to do it without a plotter would be nice... But it also requires a lot more unique skill, one that's way more easy to mess up. I know I wouldn't trust myself! I think I'd do a better job with a graphtec , so why not use one.
I can tell you if I tried to exacto that, one side would be an inch and the other would taper from an inch to .75".