I must live in parallel universe....
I've never had the Weaver system return to zero. Ballpark, yes. But, not as close as other designs. -Regardless of the level of quality.
Honestly... I've had far better luck with
rimfire dovetails returning to zero, than anything based on the Weaver system.
With quality mounts and good machining, a Picatinny rail does well. With mediocre quality or a poorly machined rail, it's a roll of the dice.
The only mounting system that I have used that has allowed 100% return-to-zero is the Ruger dovetail ring system.
Do such Q-R scope rings need to be a single unit, with the two rings as part of the same apparatus, or can you have two independent rings with Q-R levers?
You can run either way.
The platform you're using, and the amount of weight you want on the rifle, are primary factors in determining which way to go. Repeatability is about the same. But there can be significant weight difference between one-piece mounts and two-piece mounts.
Just remember, with Picatinny rails, during installation (or re-installation), to hold the optic/mount down, forward, and against the fixed side of the clamping jaws (left side usually) while tightening.