Current meta favors PROT after the spec changes. BDK got nerfed a bit on their durability. PROT is just far more mobile and a better toolkit if someone does the knockbacks on sanguine weeks.

RDRU has been a thing since launch though. It's just probably better to have two brez when so many other benefits exist. Balance this expansion has been in a terrible place with most teams just going BDK / FRMAG / ROG / DH / X (RDRU or HPAL) variant.

As usual come 8.3.5 or whatever the final patch is specs will be better balanced. Only to be turned upside down in 9.0 again. I'm honestly over it.