Without seeing the roosters- the leghorn in particular I kind of doubt that's the case. They're all very young birds to my understanding.
Not to scare the person off, the top rooster is a leghorn. It is possible he is from a line with way oversexed or aggressively sexual roosters- more than the typical rooster. Or he may be a typical rooster that happens to be dominant yet very young and may calm with age, doesn't matter if there are other roosters around or not. In other words.. there are genuinely mean and aggressive leghorns, and very average leghorns. Which type is this one..?
It seems important to the owners the rooster not be so aggressive so perhaps in *this* situation that rooster be removed if another rooster is naturally less dominant or aggressive.
Is there some way to see pictures of him?
Are the other birds hens scared to the point of screeching and running plus staying off ground to be away from this one or do they basically make a little effort to stay out of his reach? the latter would be normal with a dominant cockerel, and he should settle down once he is mature.