In my opinion, guitar is a more fluid art than singinig. KK never played the exact same solos every single night so why can't Richie play his solos from his heart? It does not affect the overall structure of the song.
There is something about a frontman's voice that brands a band, especiall when it was such an incredible voice that branded the sound. Have I heard the Ripper era stuff? Yes! I just was not impressed with the majority of it just like I was not impressed with much of Rob's Fight material, and Two? No!
It's the combination of Rob with Priest that makes the genuine sound of Priest.
Am I sad that KK has departed? Sure, but considering age, his life as it is today, and his statements on why he left; I hold no animosity toward Richie because he was asked to fill big shoes. KK made his decision and I respect that.
Do I think the new album will suffer because KK is not giving creative input? That remains to be seen and perhaps the final cuts will show us just how much KK contributed to the sound quality of Priest. The jury is still out until the new album hits the shelves. Any accomplished guitarist can play KK's riffs and Richie probably grew up trying to learn all he could from listening to both KK and Glen. But can he add to the sound? We will see.
Now, just to round out my argument about why Halford is so key, I offer you this article:
I'm not bashing anyone I just want to point something out.
Some say they don't like Ripper because he sings differently
than Rob and therefore changes the sound of Priest so he is
unacceptable yet Richie gets commended for adding his own
style and flair and thus changing the Priest sound.
Bash one and praise the other.