It's crazy how Oda's solution to broken powers he made himself is to retcon them into being less powerful.
The worm could regenerate just fine after getting sliced up in half, Broggy's arm was levitating while regenerating, Gunko practically regrew instantly even when her entire upper body was vaporized, but Killingham can't do anything about being sliced into pieces and being tied up by regular ropes.
Xebec seemingly murdered the Davy clan to take them out, and was left defenseless and unable to move from Garp and Roger's final attack, but now killing someone regularly causes them to come back completely back fine.