The abundance of fee plans are largely untouched and not used for the average builder. The files are sold though, even the free ones and I have yet to have a single person ask me for files with a file of their own they created to trade.
The nature of kit sales is a volume thing. The more selection the more options the more people it will appeal to. I see almost all of the kit manufacturers just stop after a handful of kits, and back in the earlier days, they had more of an exclusive since it was expensive along the gear.
With your 3d files, I use Blender for the design element, surely there is a format that can be imported into it from something fusion created, that would be the work around with them. I have Fusion on my laptop, it's my only Windows based machine and is largely only for very limited use, it wouldn't run on my Linux box and I loath their rates, subscriptions, restrictions and are damn nosy making you upload your files onto their server's.