Despite the ongoing cynicism and critical mauling that they received at the time, and still receive today, I believe that history will judge Stock Aitken And Waterman as they are - the Holland Dozier Holland of their generation.
There is nothing wrong with hitting on a formula for a sound, and replicating it over and over - pop stars have done that for generations, with massive success.
And it's the volume of sales that indicate the success of the formula, not critical judgement.
The sound the trio crafted carries a number of standard features inccluding very bright and splashy production, with lots of synth strings and toppy sounding synth drums over a fast dance beat.
The real skill is the musical hooks they created which were instantly memorable and caught the imagination of the teenage record-buying public in their late-eighties heyday.
Everything your friend needs to know is here -
https://en.wikipedia.org/wiki/Stock_Aitken_Waterman
https://en.wikipedia.org/wiki/Stock_Aitken_Waterman