We still don't know how archivally stable the latest RC papers are, and fiber is proven technology. I have some 20-year-old RC prints that have lasted, and I have some 10-year old RC prints that have silvered out on display.
High end galleries that sell to serious collectors show very few RC B&W prints. Maybe it's snobbery, but, hey if the snobs are your market, there's no downside to catering to it.
Personally, I don't think any RC paper I've tried really produces the blacks and the subtle gradation you can get with graded fiber papers. On the other hand, they may work for some kinds of images and some tastes.
I use RC papers for convenience sometimes, for some proofs, prints for reproduction that don't need to last a long time, and for snapshots that are for passing around more than for mounting. Prints that are important to me are on fiber.