Katy Perry is one of the most interesting pop stars of the past decade. Emerging from the wreckage of a Christian country gospel career (one album, released under the name Katy Hudson in 2005) she reinvented herself as a funny, outspoken pop diva with her 2008 breakout hit I Kissed A Girl.

Although she calls herself a singer-songwriter, she works closely with a team of writer-producers marshalled by Max Martin, the Swedish super producer who helped forge the careers of Britney Spears, Pink and Taylor Swift. Perry has all the vocal chops you might expect from a church raised singer but her USP has been her over-the-top videos built around a brazenly saucy image, establishing her as a sexy but less provocative rival to Lady Gaga.

Now, at having divorced the British comedian Russell Brand and supported Hillary Clinton’s presidential campaign, Perry is talking about wanting to make “purposeful pop” with her fourth (official) album. That clunky phrase suggests a push towards higher artistic ground but turns out to mean pop that isn’t really fit for the purpose. Witness suffers from “blockbusteritis”, the same kind of over-thinking and over-spending in pursuit of clichéd goals that turns so many superhero movies into empty spectaculars.

On the surface, it is slick and accomplished, with an emphasis on glistening electronic techno-disco grooves, plush, plastic sounds and special effects. But the more time you spend with each song, the more it sounds like a variation on something you’ve heard done better before, a formula in search of a hook.

Forty tracks were recorded and boiled down to 15 but there isn’t an original idea between them. There are so many different writers and producers involved that whatever makes Perry an individual talent has been lost in the mix. Swish Swish is a hip hop put down apparently aimed at rival Taylor Swift but too generic to land any blows.

Its boastful meanness stands at odds with the sisters-together perky pop feminism of Hey Hey Hey. Power (which Perry co-wrote with British one man band Jack Garratt) has a fierce directness and theme of self-improvement yet the slinky Bon Appetit (credited to eight writers) sees her offering herself up as a smorgasbord to be nibbled on by guest rappers, with queasy food allusions to her private parts.

For about half of Witness, Perry appears to be striving for meaning at the expense of catchy choruses. On the other half, it is as if she has lost her nerve and been persuaded to sing choruses that have no meaning. Witness is the sound of someone trying to cover too many bases. Perry has probably done enough to keep the box office machine rolling but it might be time for her to shrink her budget and make that little arty offering that really comes from the heart.