Preload can mean taking out the slop out in parts before everythings been loaded or clamped down. That's exactly what they J-tool does and applies constant pressure and prevents the parts from being cocked sideways. Rebuilding a few transmission and having only limited mileage can not definitively say it's been rebuilt to the same standards that GM intended them to be and improved upon from R&D in design flaws.
Can you rebuild a trans without a torque wrench, sure you can. Is their potential to do damage without it, you bet.
If you did read my original post I mentioned it in the recommended tools and not as a necessary tool. You should re-read what I wrote in my original post, or better yet I'll post it
Their are lots of required tools needed to properly rebuild the 4t65e correctly. You can backyard mechanic it, but thats up to you.
Tools you have to have
Tiny screwdriver for snap rings
Snap ring pliers
Some form of a clutch compressor
Teflon seal resizers for input shaft and input clutch drum (can have a local trans shop do this for some cash)
Bushing Driver set to replace bushings
Valvebody reamer to implement TCC fix
feeler gauge
Lots of other recommended tools like a bearing puller, final drive clearance checker and so much more.