The problem with counting on just the pocket is that you’re failing to account for any variation in the RMR itself. If you want a cut “perfect” enough to eliminate the recoil bosses, you have to send the optic in with the slide so they can fit it. Which means if you sell them separate from each other you’re effing over the next guy, or if you change optics you’re effing over yourself…
Not in my experience. With most other optics, yes. But the RMR external dimensions are nearly always consistent enough to work in a tight pocket.
I'll point out one of my G19 slides as an example. It was milled for a tight fit with an early type 1 RMR, and used two others in that slide over the years, no changes or fit issues. Then when the Type 2 came out, right within that first few months or so, I picked one up and found that they were .003" longer. Note that .003" is significant enough to be noticeable as an issue; that speaks to the consistency of the earlier optics.
So at that point I did have to go back and mill .003" off the back of the pocket. Then I had an issue with that RMR (the tiny lens over the emitter fell out) and sent it back to Trijicon. Same issue with the replacement, and the next 3 after that. They did eventually change the bonding around that lens and fixed the issue on the last one I got, but the significant point is that all of those optics fit the cut the same way.
So no, with this particular type of optic, the bosses are not necessary, and the cut can be tight enough to constrain the optic very well. Heck, we were using milled slides with RMRs in them for nearly 10 years before anyone decided they "need" bosses. The obvious caveat is that .003" difference between type 1 and 2 optics, but if you're sticking with a new optic you're good to go. I've had a lot of RMR sights on a bunch of different pistols, and have never had one fail to fit with the exception of the type 1 - type 2 change.
However, that is the only example I know of where the slide pockets are adequate. Everything else out there needs to have bosses, but the slide pockets also need to be milled oversize so that the optic can be replaced. Regardless, even then you don't need both locating studs and screw hole bosses. Too many dimensional constraints means either the parts don't consistently fit, or some of the constraints serve no purpose (except advertising).
That is my first hand experience.