My take on PAS is slightly different, but I think we all may be able to agree on the starting point, which is cadence based PAS is a “dumb” system; not stupid, just not very intelligent. Sort of like how a manual transmission has no built in logic versus an automatic, that down or upshifts based on conditions it is able to determine on its own. With cadence based PAS, it's faster pedaling, more motor contribution, period.
The user has direct access and control over other variables on the bike, like throttle, changing PAS assistance levels, gearing, and of course his/her cadence. He/she also has visual and other sensory inputs, to see the grade the bike approaching, and feeling a head, side, or tailwind. The user can also place the PAS level to zero, and use throttle only, to go full manual (throttle only). A torque based PAS, while better, still leaves other variables in the user’s control, like gearing (not pure manual or auto, but like an automatic transmission with paddle shifters; sticking with the car analogy).
If you think about it this way, the PAS, in any form, is not only pedal assistance, but user assistance, since it handles some of the logic or intelligence applied by the user, over full manual. Cadence PAS being the dumbest, and torque based PAS being a little smarter. The latter should be able to deal with things like head wind or increases in grade, by applying more assistance automatically under those situations, alleviating the user from having to make the adjustment the throttle would provide.
As long as the PAS is not adding too much assistance based on the user’s preference, at the speeds the user prefers to travel on flat ground, the user can choose to use the small amount of logic built into a cadence based PAS, even if it isn’t much. In other words, the user may either prefer to keep their portion of contribution steady (e.g. user contributes 200 watts) or keep the motor’s contribution steady (e.g. motor contributes 250 watts); by controlling the other inputs, like PAS level, gearing (which affects cadence) or pedal effort. He/she supplies all of the missing intelligence to meet that goal. If the user approaches a hill, he/she can increase the PAS level or downshift (increase the cadence), and the “dumb” PAS will increase the motor contribution. Or, the user could just pedal harder, to keep the motor contribution steady, but at some point will need to up the PAS, downshift, or use the throttle, once the hill becomes too steep. Just as a user can learn to use throttle for everything, it’s possible to use even “dumb” PAS for everything, taking advantage of its rudimentary logic.
