It might not fail rich but it can get stuck there when it's almost dead. No input is more accurate than a bad input.
I've been monitoring my vehicles' stock o2's for basic tuning (along with an EGT gauge) since 1993 and I've used an Innovate wideband for full ECU tuning since 2004. In fact, for Subaru tuning, all fueling tables are done with a target AR which requires you to first dial in the mass air flow meter with a wideband or everything will be wrong.
