I would think a big block in a dart probably would do fine without the need for the kick down very often.

A slant 6 or a 318 in a B or C body is a different matter (especially in the 70s when lots of cars got stuck with 2:76 or even worse, the 80s with 2:45 gears).. That part time kickdown was a nice addition. You didn't have to floor it every time to get the trans to downshift for that extra kick.
it made a few powerless slugs at least somewhat drivable.