I feel you. Assembling ARs like legos is not gunsmithing. It's fun but not satisfying.
Bolt guns are a lot more fun if you own a mill and lathe, but even they are simple.
I like firearm mechanicals, like scratch built AR gas systems, buffer systems, and the like, because it's a chance to design, make, and tune a system that is balanced and benefits performance. I make stuff for myself and don't want to go into business or really "do" other people's stuff, it's my hobby for me. Keep your lawyer out of my shop. I do a lot of these projects, and end up writing or posting very little about them for one reason or another. It's more my style to just hand someone a toy at the range and say try this, then show what I've done.
I have been taking a good hard look at the possibility of scratch building a Lemat revolver modernized to shoot rimmed cartridges and a 3" shell. Any part not possible to make on the mill and lathe can ultimately be made with a vise and file, just like the originals.
I also like to look at other ideas on the dry erase board on the backs of my eyelids, like how cool would it be to build a takedown lug for a SKS to make a 6-lb backpack carbine good for 300 yard coyotes?
Back in the day, guys like us would pick up cheap Springfields, Enfields, and Mausers, and turn them into completely different sporting rifles. No reason we can't pick up where they left off, with a whole generation of cheap surplus out there. Why not get a Polish PP-Sh parts kit and chamber it for 9mm NATO with a rail accessory system? Heck, chamber it for 5.7FN, why not? Anything is possible.