Damn, that's very interesting. So Zuk really is as strong as Bandos in terms of raw power? That's very inconsistent with the tiers 6 and 3...and by extension, the WG would also be as strong as a T3 god...I'll chalk it up to a lorefail. Still, I like seeing god wars military tactics being discussed.
I don't consider the old god tiers system canon. The main reason for this is exactly what you've laid out here - it encourages this sort of meta analysis and "X couldn't possibly Y" which is antithetical to storytelling.
It's a tricky thing to formally retcon in-game because it was never defined in game in the first place. At some point though some authoritative NPC will say "you may have heard that the gods can be strictly defined and categorised - this is not the case".
Besides that though, my take is that Zuk could not have ultimately defeated Bandos in a straight fight. Bandos was more powerful. However, Zuk could never be defeated, so Bandos had to come up with a plan to imprison him.
The god tier system in fact wasn't an in-game thing at first. But then Zamorak went ahead and referenced it in post-quest dialogue for Dishonour Among Thieves.
He did, but to understand what he's saying you need to reference the out of game information.
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