Nevermind, lol *rubs back of neck*.
If Danzo was nowhere near Hiruzen's level, they wouldn't be able to compete at all. And no, they were rivals in strength; they both were going for the title of Hokage and Hiruzen won that because of his acceptance to be the decoy for the rest of the group (the Will of Fire).
Oh? Does it not? Are you assuming that the Senju clan won the clan wars through numbers then? If they were so high in numbers, how did they die out so easily? No, the Senju clan won through having brilliant shinobi, and if Tobirama is the second-best of the clan in their prime, then he is deserving of high-Kage level. If his weakened Edo version of himself is considered Kage-level after displaying but just one jutsu, then he's obviously high-Kage level in his prime.
So what you're trying to say is if Gai was a shinobi during the First Shinobi World War, after the First Hokage died, he himself, Maito Gai, would be the Nidaime Hokage?