Well, if we want to go by the titles Killer has more reasons to get an higher percentage of his Captain's bounty (more than 30%) than Marco, King or Katakuri.
These charachers fall under the category of RHM/1st Commanders, while Killer has a position much more reletable to Rayleigh or Beckman for example since these are considered First Mates/Vice Captains/Partners and we all know its a pretty different category. Beckman, for example, will most likely get 1,800,000,000 - 1,900,000,000, hell maybe even 2,000,000,000. These are numbers that correspond to 45% or 50% of Shanks bounty...
We don't know Rayleigh's either but wouldn't surprise me if he's in the range between 2,300,000,000 and 3,300,000,000 seen all the years of service and being the VC of the former PK. These numbers correspond to a minimum of 41% and a maximum of 59% of Roger's bounty (even tho he'll probably be under 3,000,000,000).
So what I disagree with at the core is that people expect Killer to be treated, in general, like a RHM or a 1st Commander when in reality he's a FM/VC/Partner and that is a pretty remarkable difference in hierarchy, authority and individual growth rate.
This is why I expect Killer percentage to be between 35% and 45% of Kidd's bounty rather than between 24% and 30%, like you said.
I agree on the fact that Heat/Wire shouldn't surpass the bounties of Franky/Robin/Brook and I think Oda will just hand Heat 200,000,000 or 300,000,000 at most.
But I disagree on the last thing you said. Luffy, Kidd and Law bounties being equal make plenty of sense since Oda decided to count Luffy's influece over the world as a separate factor (with the Yonko title). We could open a discussion about this but it's not the right thead for it so better not do it here...