Lapping skeptic here even though I understand completely what you are saying and why. I’m curious your take on this— the sort of variation you’re talking about is going to be potentially different every time the rings are mounted in a slightly different position fwd/backward if you are using a pic rail (and probably even with a direct mount), especially if you are mounting the same rings on multiple rifles in the process of switching scopes back-and-forth. Do you lap every time you remount the same set of rings? or do you simply not switch rings around? Or do you not see this variation in mounting position, only variation in rings themselves and 1 “lap” fixes it? Or do you leave the rings with the rifle, and only switch the scope itself.
Ie, What’s your take on lapping rings that are going to get switched around quite a bit?
There are some variables, and I'll share some of that in answering your question in a moment, but for me personally I actually don't switch out scopes or rings at all - my intent is that it will be a permanent and complete setup, unless something either breaks, it unexpectedly turns out to be unacceptable to my needs, or I decide to upgrade the scope. The only exception to that is a Bobro QD mount I have on one of my ARs, where I swap a LPVO and a thermal unit back and forth, and each of those units goes into the exact same pic slots every time (witness marks on the rail for each).
The Bobros are a bit chonky, adding to their stiffness, which is part of why I believe I'm not seeing any POI shift in QD swapping them out. The upper too is a very high-end, precision machined piece - I might be getting very different results if I was using stuff with less precision in the machining, or with a lightweight aluminum mount that had more flex. But I still had to lap that Bobro, in place on the gun. Not much, as it's pretty precision stuff, but it still required it.
With my bolt guns, when I mount the rings it's meant to be permanent - I scribe the footprint of the ring base onto the receiver, rough everything up on both mating surfaces with 600 grit sandpaper (or something close to that), and usually affix and bed with JB Weld. If not that, then one of several permanent Loctites. After that's cured, I'll lap the rings to make sure they're trued in place and under that torque (fasteners also Loctited in different ways), and then bed the scope into the rings using Loctite 609 - it's one of their green ones, meant for bedding cylindrical objects. It's not a permanent bedding like JB Weld, and a scope can be removed and the 609 film removed as well, but it does bed and provide some adhesion.
So, for all these reasons, I view that setup as permanent, unless the other reasons mentioned above come up. I can still remove the scope if needed, and would give the rings a pass with the lapping kit to ensure the 609 is out, but would have no problem from there putting a new scope in. The rings, however, I'd be loathe to swap out - those have been trued to the gun, on the gun, and are best left in place. If, I absolutely had to swap a set of rings out to a different gun, yes, I'd mount them up and then lap them again in place (using dykem, sharpie, etc to know what material's being removed). The more precision all interacting parts were machined with, and the fewer fasteners involved, the less you can generally expect to need to lap.
BTW, part of why I don't swap my scopes around is a bit related to a personal philosophy I have - I don't own a ton of guns compared to most guys, but when I get a new one I build a complete setup before spending another dime on any other gun, gun part, accessory, or whatever (a few inherited guns excepted). That new gun gets exactly the glass I want on it, exactly the accessories, and at least a 1000 rounds of selected ammo for it on my shelf - I treat every gun as though I might need to spend the rest of my life with that one, and only that one, before investing anything into a new one. Given where I live, I'll go months shooting daily - often only 10-20 rounds, and about 10x that in dryfire when I'm working up my skills on a new gun, but I put a lot of time on the range with each one of these. When I add a new gun, it's to either fill a role that I haven't yet, or it's a significant and specific upgrade over one I already have. That's where I personally get the most satisfaction - the process of it all.
But that's why I don't swap scopes around - it's a lot of work to mount one properly (precision, durability, reliability), and I just don't buy a new rifle without also having the cash to put exactly the glass on it that I want.