We aren't completely finished with the 7.2.5 gearing strategies -- we're still tweaking rotations and our entire gearing strategy system.
There are a lot more viable combinations of stuff in Legion compared to previous expansions: talents, legendaries, set bonuses, trinkets -- it is literally impossible to make a "one size fits all" gearing strategy anymore. That's why we're hard at work on the new system that will have hundreds or more for each spec, and we automatically choose the right one for you. It just isn't done yet! We're going to be making a lot of announcements about that over the next 1-2 weeks.
In the meantime, the reason that you're seeing ~3% margin of error instead of the usual ~1% margin of error in this case could be any of:
- the default 7.2.5 strategy we created is using different talents than you
- the default was based on different legendaries, which can color the results a bit
You can create a custom strategy for yourself, that would give you better results right now -- just search for "custom strategy" on the forum, we have a tutorial.
Or, wait a week or two for us to implement our new system that can auto-adapt to any combination of talents, legendaries, and set bonuses.