Having the middle lane/lanes be the “passing”/speeding lanes is less safe though, because both outside lanes then have to worry about faster traffic merging into them to pass people in the middle lanes, rather than just a single lane. Also the people merging absolutely would still have to deal with fast drivers, when drivers in the faster middle lanes try to pass each other on the right. Doing so would put them in the same lane people are using to merge onto the highway.

Edit: also people in the slower left lane would have to merge into and out of the faster middle passing lanes in order to exit the highway, which just sounds like a recipe for disaster.

Edit edit: are you talking about 4 bidirectional lanes, with, for example, two going north and two going south? If so my bad for the misunderstanding, we actually agree