You're overthinking your work process IMO, and I do get what you're hoping to accomplish. I've been building bridges and buildings for over 20 years, and can tell the difference between a 19mm bolt head and a 20mm bolt head from distance. Seriously.
For what you're describing, I use the scanning engine in the latest version of Illustrator and an inexpensive scanner. Scan the image (be it a real object or a drawn sketch on graph paper), and use Adobe Illustrator's tracing engine to create a usable (and scaled) object to work with.
Wacom's driver does provide a "full" or "1-to-1" mapping system that is completely independent of the OS, and using a Large or Medium or Small Wacom tablet is NOT going to change the scaling issue you're concerned about. Wacom tablets are not digitizers, but Wacom has purchased much of the IP of digitizing-related companies that have gone under over the years. And, FWIW, I helped design and build out 3 light rail alignments that are in operation today - with software drivers created by companies whose IP is owned by Wacom.
I'm not a huge Wacom fan of late. I really liked the solid Japanese-made tablets made in the early 2000's far better than the creaky Chinese-made stuff for sale offered now. I've told them that (they're in Vancouver WA, and I'm across the River in Portland OR). And, they do make a large tablet I wouldn't want to be hit over the head with. Or, work on a daily basis...

But, the large tablets are huge - see one for yourself and you'll see what I'm alluding to.
Cheers!