You should read what I wrote before so quickly assuming that I don't know what I'm doing. I said getting a stable AFR at WOT is 'an exercise in frustration', not that I can't do it. Changes in lambda in M4.4 can't always be traced in KFLF, as instabilities in AFR don't always follow RPM vs Load, so changes instead have to made to MLHFM - this is of course after a properly calibrated FGAT0 (KRKTE equiv) and TVUB and after tuning KFABAK, KFAVAK, KFBAKL, KFBAW, KFVAKL, KFVAW, KLWF (wall film model). With adequate logging and iterative modifications to MLHFM and KFLF I can get stable and repeatable AFRs at WOT, it just takes a lot of work. For remote tuning customers with novel setups, it's not practical to get this amount of information.

One real world example for why wideband regulation at WOT is helpful - a lack of manifold reference to the FPR. I've seen multiple customer cars that have had the vacuum line pop off their FPR, but the change in fuel delivery wasn't enough to set a P0171/P0172 code. At WOT their AFR would have leaned out, but the wideband routine kept it in check.