I believe at the time they didn't go with the Aussie option is when they first started to upgrading theirs the gubberment of the time hadn't decided what they wanted and in turn, watched and learned how the Aussie frigates turned out, while capable does have a top weight issue and so ballast added reducing speed and CoG (this we all know) ... and also at the time most likely budget... (which now in hindsight probably would have been cheaper per frigate lol)Is it (one of) the reason why RNZN did not adopt Australian version of modification? RAN's ANZAC class modification apparently looks top heavy. As you said, RAN's large mast with AESA radars on the top, added with significantly improved wiring, analysis power of CMS, and "quad-packed 32 ESSM in their Mk.41 VLS" shall be very heavy. Compared to that, RNZN Te Kaha and Te Mana "looks" much more "stable".
#or RAN is handling it with adding ballast? Losing fuel efficiency but keeping CoG balance?
The other thing is the Ross Sea and the Southern Ocean while the Aussie frigates handle it ... Ohhhh kaaaaay, they aren't the best but neither were the kiwi frigates. Hence Project Protector and the 2 OPV's. (Also the Government realised 2 Frigates can't be in 4 places at once... lol (Read into that what you will lol.)
The Kiwi frigates were faster, and were more stable I guess time will tell how this is post upgrades.