I've been a subscriber to Which? for many years - as an audio professional for 60 years, I find their reviews of audio equipment woefully poor. And I assume that their motoring reviews are equally lacking... after all, this is an organisation for consumers, who have axes to grind, so you'll find that, just like this forum, there will be a core of people who have had bad experiences with their cars and report those, while many many others are quite satisfied and won't bother to comment.
For me, the LKA issue is no worse in the MG than, for example, in the VW EVs, which I've driven - and there is no chance of MG allowing drivers to switch LKA off permanently until the NCAP guidelines change.