To reply to your points though:
A) Gillen has more than a wider range. He has more control and better technique. Why do you think Martin fucking blew out his voice around Cross Purposes and Cross Purposes live? Why do you think that live, Martin had to "cut corners" and sing some sections lower, or rewrite entire vocal melodies to fit his quickly-lessening range (Compare Anno Mundi on album to Anno Mundi on Cross Purposes Live. Compare When Death Calls on album, to When Death Calls on "Headless in Vienna '89". Etc.)? The answer, improper technique. This alone invalidates your point that Martin is the best singer Sabbath ever had. Claim he is all you like, but the fact of the matter is that this is simply fucking wrong.
Its okay though. Its everyone's basic human right to be wrong.
B) Ozzy and Dio Sabbath are infinitely more artistically relevant than anything Martin ever sang on.