There was moment last night when Katy Perry was being swallowed whole by the biggest pair of lips this side of a Rolling Stones' concert that I leaned over to my wife and said: "This is bonkers". Predictably the Mick Jagger-like lips were for Perry's breakthrough hit from 10-years ago, I Kissed A Girl. Less predictably, Jagger appeared to eat Perry, without really chewing.

There was also a moment during the sold-out Monday night show where some human-operated pink flamingos of a similar size to the Jagger lips were running around and I may have uttered the same word: Bonkers.

Evidently a little devoid in the vocab department when I'm being overstimulated like this, my scribbled notes then tell me I went and described the point where Perry's eight backing dancers were all wearing old-fashioned TV sets as heads as being "bonkers" too.

Not to mention the massive tiger, the floating planets, the enormous moving hand that appeared from nowhere, the freaky large roses, the basketball hoop fit for the BFG and essentially, every highly choreographed minute of this two-hour, Cirque-du-Soleil-meets-Alice-In-Wonderland-meets-Abba-meets-2001: A-Space-Odyssey, spectacle.

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Even Left Shark from the 2015 Superbowl was there.

So yes, seeing 33-year old pop megastar Katy Perry live in 2018 is a little bonkers. It would've been bonkers in 2017 as well, because that's how long her Witness tour has been going. In the 11 months that have followed, she's played well over 100 concerts (of identical set-lists) to roughly one million fans in every continent on the globe. On the face of it, staggering numbers and not bad at all for tour in support of an album that even in the artist's own eyes, was a disappointment.

Which begs the question, if Perry herself is unsure of Witness the album, why is there so much of it on Witness the tour? Ten of her immovable set-list's 21 songs are off Witness and the sheer amount of time devoted to oddly tuneless tracks like Swish Swish and Bon Appetit – her first two songs to completely miss the US top 40 – suggests that elaborate staging and effects are more important than the songs.

Australian critics were harsh, suggesting the glory days have passed for one of the most statistically successful artists of all time (Perry's the only artist to have six different songs sell over five million copies in the US alone). I'm more optimistic because any artist with a long career will have highs and lows, but as those reviewers have pointed out, ticket sales are almost exactly half of what they were for Perry's 2014/2015 Prismatic tour.

At the same time as Pink kept adding more and more shows to keep up with her insatiable Australasian fans, Perry had last-minute tickets going for $70. So what's changed?

In many ways, Katy Perry has always occupied a slightly curious place in the pop landscape. She has bigger hits than Beyoncé and Taylor Swift and arguably broader appeal than Rihanna and Lady Gaga (but not the concurrently touring Pink), and yet in some ways, it's as if she's not entirely certain of who she wants her audience to think she is. Is she a sex kitten or a heroine to pre-pubescent girls? Then at the same time as she makes public comments about wanting to make mature, "purposeful pop", she releases an X-rated double entendre that references non-food related buffets, Bon Appetit. Goodness!

But because of the (mostly) inoffensive joy of her long list of radio smashes, as well as an overriding image of cartoonish good times from the first half of the decade, a Katy Perry crowd is still dominated by parents and their young children.

"I go to concerts too! You don't want the B-sides, you want the hits!" said Perry (in what was to prove a fraction misleading) after the bombastic pop perfection of Teenage Dream's title track, a song so scientifically irresistible in its structure it's even studied by university music students.

Teenage Dream occurs as part of a run of seven smash hits in a row (Dark Horse, Chained To The Rhythm, Teenage Dream, Hot N Cold, Last Friday Night, California Gurls and I Kissed A Girl) that remind just how hooky and fun her best work is. Unfortunately, they also serve to draw attention to those less memorable tracks from Witness like Déjà vu and Power.

With Perry's easy charisma and live vocals that are stronger than many of her pop peers (you wouldn't get Britney belting out an a capella snippet of All By Myself as an ode to Celine Dion), the at times muted audience response suggests all the outrageous sets are verging on being a distraction.

If there's a sweet spot between the theatrics and the actual music itself, it came during 2012's Wide Awake. Finally stripped of much of the noise of the mostly faceless band and the almost digital-like backing singers, there was Katy Perry, strumming her guitar, singing from the heart. While on Saturn. It was great. Still a little bonkers, but just the right kind.

• Tim Roxborogh hosts Newstalk ZB's Weekend Collective Saturdays and Sundays 3pm-6pm.