For plot/story development Oda does the stupidest or incoherent shit that he wants. The most recent example of CoC being the answer for HKs. Now this was not absolutely stated (the official will clear shit up probably) but it was heavily implied when Gaban talked to Luffy about how he uses ACoC and immediately follows up with saying that the HKs are not immortal. Then we also get Loki saying that he now understands what his power is and that he too can fight the HKs. And then we get Gaban talking to Zoro about recognizing and using ACoC.
The problem then becomes that Gaban knows how to hurt the HKs, he has history or is known to Sommers. If Gaban has CoC and he knows that with ACoC he can hurt HKs then why did he not use it against Sommers. Weirdly the panel with most likely ACoC usage is his FS panel where he attacks Gunko. So we have a few options on what happened in Gaban vs Sommers fight.
Gaban does not have ACoC
Gaban is rusty and could not use ACoC like he wanted/it was weak
Gaban has ACoC but chose not to use it against Sommers
There is regen limit and with ACoC you can get to that point quicker
The last one is probably a valid option since we see that Sommers did not immediately regen like others and that he is feeling the pain/has taken damage but is still regenerating because the regen limit has not been reached.
The problem then becomes that Gaban knows how to hurt the HKs, he has history or is known to Sommers. If Gaban has CoC and he knows that with ACoC he can hurt HKs then why did he not use it against Sommers. Weirdly the panel with most likely ACoC usage is his FS panel where he attacks Gunko. So we have a few options on what happened in Gaban vs Sommers fight.
Gaban does not have ACoC
Gaban is rusty and could not use ACoC like he wanted/it was weak
Gaban has ACoC but chose not to use it against Sommers
There is regen limit and with ACoC you can get to that point quicker
The last one is probably a valid option since we see that Sommers did not immediately regen like others and that he is feeling the pain/has taken damage but is still regenerating because the regen limit has not been reached.