If you're talking strictly about the best singer from a Seattle band, none of the vocalists listed come even close to the ability Geoff Tate could do in his prime. I guarantee you he could sing any of these songs by the "grunge bands" (although I don't know why you'd want him to) but they would have had immense problems even attempting to sing his more challenging songs like Take Hold Of The Flame, Walk In The Shadows, The Mission, Suite Sister Mary, or Anybody Listening. Cornell had the range to attempt some of these songs but no the tone because he sounded screechy in the higher ranges while Tate had a powerful and still clean voice. Can you imagine any of these grunge singers attempting "Roads To Madness"? Cornell is the only one who might possibly have been able to hit the notes but as far as tone and timbre and doing it in a clean voice, forget it.
If these grunge bands wanted to cover the best Queensryche songs, again the instrumentalists would have had extreme difficulty. Cobain would never have even gotten out of the starting gate whereas Degarmo or Wilton could play Cobain's guitar parts in their sleep.
It's no mistake these bands all come from Seattle. After the success of the Empire album the record labels sent their agents to Seattle to sign more bands like Queensryche. They couldn't find even one. So they went ahead and signed grunge bands since there were plenty of them in Seattle since it doesn't take a rare group of musicians to play grunge like it does to write and play Queensryche music. When you lower the bar for ability by so much, then of course you find many more musicians who have the requisite ability to meet the new, lowered standards.
Can you imagine Cobain, Vedder, Staley, or even Cornell attempting this? The variety of voices needed, the clarity, cleanliness and rage with full power required would make it a nightmare for any grunge singer to attempt. Even their bands would have been humiliated in attempting to perform an accurate rendition of this classic: