I would need more details to look into this one. Our default gearing strategy doesn’t try to get mastery. Maybe you have some filter or options set that is constraining the gear to some choices that is causing that - like if you were only looking at a few bosses in a higher difficulty, and those bosses just happen to have mastery on the gear they drop. Just an example of how that could possibly happen and still be a correct suggestion.
The old AMR was simpler… but gearing was also simpler. What AMR does now is a lot more complicated, but still accurate. The problem is that it is harder to understand, at a glance, WHY Mr. Robot picks what he picks. Other sources of gear advice are still trying to shoe-horn the gear optimization problem into simple rules of thumb. That just doesn’t work very well anymore. There are many combinations of gear/stats that can all be optimal.
Our data-driven approach to theorycraft is good at finding ALL the good options, and then picking the best one for you, based on your settings. And, our approach is particularly good at finding gear solutions that are not obvious. The “simulate” button allows you to test our advice and easily determine if the advice is correct or not. It’s a little harder for Best in Slot, since you’d have to figure out what to compare it to… in your case, if BiS got less mastery, what would it have to sacrifice to do that? Item level? A set bonus? A good trinket proc? There are so many variables now.