I'm sure most fans consider Ian Gillan as the "voice" of Deep Purple. But, IMHO, Burn was a fantastic album and the addition of Coverdale and Hughes was a seamless transition. But these two artists were only band members for three years (3 albums) in the course of a very long existence of the band. Again, IMO, DP's best and most successful work was produced by what's known as the Mk II line-up with Gillan. With that said, some of my favourite songs are from Burn, the band was able to continue without missing a beat.
I find it odd and don't know the circumstances of how Glenn Hughes is able to retain the name "Deep Purple." At least his live show only includes music from his time in the band up until present day.