As much as I love Glenn (since I was a kid hearing my brother's Deep Purple album) as much I can't stand him "alone"..for me he will always be "the other higher pitched soul voice/counterpart" of David's deep soul voice on these legend three Purple albums..
Male singers like him need "a deeper counterpart".Ofcourse always in my very personal opinion.But I can't stand such high pitched male voices.One reason I could never really dig Rush or Pawlov's dog.
Of course, I respect your opinion and it is obviously a matter of taste. However your explanation ("higher pitched soul voice/counterpart") is a bit surprising to me. There are probably other opinions like yours but I'm reading this for the first time.
I listen to a lot of music, 95% of which is guitar based. There are a lot of good singers in rock / metal - many can't be compared to each other because they have different strengths - but for me Glenn stands out. Because his voice is amazingly intense, a living-breathing thing. Strong and thick, but also incredibly soft, sensitive and expressive at the same time. His voice is quite unique and the way he handles it is outstanding.
And the fact that he can do it even in his age is unbelievable. Plus he has a ton of records during his career so there will always be something to listen to.
Sorry, it's not for you but I must have to show: