Not sure if there can be a "Kameo Tier List".... My suspicion will be that their effectiveness will depend on the main you run with them. I belive we will end up with a Kameo Tier list for each main, and then a "Competitive Tier List" which lists Mains+aKameo as "one combined entity". So Sub might be on the list twice as there are two competitive variations, and the Kameo will determine which sub is higher than the other.
In short... arguments about tiers in this game will be even more pointless and stupid than ever before.... and by stupid I mean there will be so many permutations that no consensus can be reached, well, even less of a consensus than normal I should say.