These weak slip and grip systems should be called All Wheel Assist and not All Wheel Drive.
How about the ones that monitor various sensors and engage the rear wheels before slippage is detected? (They will also engage the rear wheels whenever slippage IS detected.)
I'm used to full-time awd, and then got a similar vehicle that's a slip&grip fwd, but has the predictive system. I'm impressed at how well it works. Probably 90% as good as the full-time awd. Never had a "normal" slip&grip awd, so I don't know how that would compare.
But, that's for light off-roading. For highway driving in bad/winter conditions, I think the full-time awd is far better than predictive slip&grip. And for highway driving, normal slip&grip may as well be fwd.