That's not zipper merging. That's just poor merging. I guess technically you can zipper merge on a ramp if there is traffic, and like you said you'd want to use the whole acceleration lane even though you won't be accelerating in traffic.
Zipper merging is when 2 lanes goes down to 1 lane
It is better for all cars to use both lanes completely until it gets down to 1 lane.
People don't understand it in the US.
If a mile down the road you see it going to 1 lane. You shouldn't try to merge over soon. You should drive all the way down in your lane and merge at the last moment.
But you'll get a mile long single file line of cars and the few cars that pass are considered assholes trying to cut to the front.
If you broke up that mile long single file line and had two 1/2 mile lines in 2 lanes that zipper merged. Everyone would get through the bottleneck faster.