I've always thought 2016 was New Zealand's strongest year in super rugby. You had the canes, winners that year, the chiefs still had rennie, the highlanders had Joseph and won the previous year, and the crusaders made big strides that year - easily their best under blackadder. People said the blues were crap; the blues had been crap for some time and it was going to take a lot to turn that around, but umaga got them passionate in defence and they were actually pretty good - they just didn't look it because the format back then meant playing a lot of games against New Zealand sides, and the other New Zealand sides were very very good that year. The blues actually only lost one game to non New Zealand opposition that year (despite apparently being horrendous), and that was to the lions who made the final (also made the final the next year), but they only won one against New Zealand opposition although they had a lot of close losses.
After that the highlanders lost Joseph, the chiefs lost rennie, the blues didn't make progress the next year then had a season full of injuries (18 concurrent at one point) and lost a lot of their key players including kaino, luatua, and faumuina and then had to rebuild.
The Australian teams weren't great, they'd been depleted by trying to stretch to five teams even though they had clearly gone downhill after adding their fourth. And then having to play very good NZ turns really hurt their confidence, making things worse.
The 2020 super rugby aotearoa season was intense, the aus one wasn't, and you really have to play top sides to understand the required level. The Aussie teams needed to be taught a lesson in 2021 in order to improve.
But let's not pretend too much here, they are still lagging, and NZ teams weren't as good this year, with the exception of the blues .