I guess the definition of "milking the system" vs making the most of various FFP whilst playing within the rules is one that is somewhat subjective. Having a varied travel schedule and multiple FFP programmes has enabled me to credit to those that earn the most points, which has been beneficial historically (*G or Oneworld, or Skywards). When I fly domestic on AirNZ it gets nothing on other *G but a tiny amount in Airpoints. When I fly other *G carriers internationally it often earns no Airpoints (or minimal).
I chose to keep *G outside of AirNZ, and my incentive for accruing any Airpoints is now diminished (or accelerated). In a similar situation to Thai-Kiwi, my lounge access etc problems would be solved if I just use my existing *G, forget about Airpoints, and I forgo earning any points on domestic travel. Also then a pain to use the AirNZ app. Alternatively I switch all travel to Airpoints in order to earn NZ*G, likely at the expense of my other *G membership.