There have been two BMW awd systems within the past 10 years (as far as I know/as far as the US market is concerned).
The E46 came with a 40/60 split system. I don’t believe it adjusted power between the axles. This system was also used on the X5 before they were updated in 2002, or whenever the X3 was bestowed onto this world to take Suzuki’s crown for worst riding small SUV. The new system, cutely named xDrive, adjusts power between the front and rear axles and stops individual wheelspin via the stability control. I’m guessing if it was a new 5 series that it had xDrive. I can’t imagine it could be any worse than the mounds of other AWD systems that have similar designs. I think many of the views on BMW’s awd system may be founded on opinions formed based on the old system(s).
Many, many companies don’t design their AWD systems in house. VW/Audi, Volvo and Ford use Haldex. Honda used BorgWarner for their larger SUV’s and the Ridgeline, and then again for SH-AWD. Anybody remember when VW and Audi’s AWD systems were different? I think it was called Synchro. I’m not sure who BMW contracts, or if it’s an in-house design.