A lot of different versions of Bonzer bottoms in the 3 and five-fin designs, with the Campbell brothers' design being the original...and even that one's gone through changes. To read the Campbells' theory, you're redirecting water to the single fin and improving hold (sort of like a canard). Personally, I think the stories of them only liking bigger, hollow waves is based on the era's quintessential single-fin board design that the original Bonzer fins were placed on. Those boards held a straight line and purely used the wave's power for speed.
LB mentioned the channels and they have evolved. At the same time, the planshapes and "v" found in contemporary tails are more geared towards the surfer generating speed by transitioning rail to rail. Malcom uses contemporary designs (fish, egg, hp) in some of his Bonzer models. Others do as well. I think it creates some confusion in "what a Bonzer is suited for". My humble opinion is that the fins of the new Bonzers are part of the equation.
In the end...it's all about the amount of hold and release designed into the board...regardless of the number of fins. Just my opinion.