They do, but in my experience most really broad generalists don't sufficiently fit into any given box. (One interview loop at a FAANG I was asked to come back three times for three teams--one systems, one backend, and one mobile--andmy backchannel feedback was "they all worry you'd get bored." Which was probably true.

There are definitely generalists at FAANGs, and they've got license to kill, but it seems like they were hired specifically at a certain rarefied level or they grew into the role over time.