The fact that higher overall growth rates are detrimental to the pathogen also reflects the impact of antibiotics, because of the proportionality between beneficials' growth rate and antibiotic production rate in the model
http://plosbiology.org/article/info:doi/10.1371/journal.pbio.1000345#article1.body1.sec2.sec4.p4

I am interested in the statement that "higher overall growth rates are detrimental to the pathogen...."

I'm not sure exactly where this result shows up in the figures, but it would seem to be based on figure 6B, where the sensitivity of rB is greater than the sensitivity of rP. Is that right?

In other words, if the coral host simply increases total resource availability, and assuming that the resource is equally nutritionally beneficial to mutualist and pathogen, does this still benefit the mutualist more than it benefits the pathogen? And if so, is this because the mutualists hurts the pathogen in two ways: via both exploitation and interference competition?