This thread may be a pig flying contest, but the basis for the debate is incorrect.
If the 'main trunk' inlcudes WLG-CHC, then there are NOT two 737 operators on that route. QF services the route with an Origin codeshare. Therefore we One World SLF's have a choice between NZ 737's and Origin 42's and Jetstreams, which is really irritating.
Origin also go to Queenstown with the 42's. According to my calculations 3 ERJ's would only allow them to operate on those two services - which are not 737 competitions at present, and nor do they involve regional airports.