It's not impossible to be a top-tier without CoC, but there should be an ability to compensate the gap because all non-DF top-tiers also have top level stats in other categories that matter, but they still need it to stand where they stand.
I mean Rayleigh/Roger should be every bit as lethal and good with non-CoC Haki as Gaban, so if Rayleigh/Roger still needed CoC to be at the level they're in, then Gaban should have ridiculously better raw stats, CoA or CoO than RR to be comparable to them or he has other abilities to balance the power or he's weaker than them while still being a top-tier.
I mean Rayleigh/Roger should be every bit as lethal and good with non-CoC Haki as Gaban, so if Rayleigh/Roger still needed CoC to be at the level they're in, then Gaban should have ridiculously better raw stats, CoA or CoO than RR to be comparable to them or he has other abilities to balance the power or he's weaker than them while still being a top-tier.