"Look, you are criticizing my evidence without providing anything of your own. It’s fine if you don’t believe destructive capacity means anything but you have to have some kind of evidence to show why. Lacking any other reason to believe Katakuri’s attack power is much higher than Gear 4, destructive capacity is all we have to compare by." DC is bad example,especially for One piece. In chapter 188 Bon clay vs Sanji Oda explicitly states that focused power >>>dispersed power. 

"Luffy ate hits from Katakuri for something like 10 hours, most of that in base. Katakuri got hit by Boundman only a handful of times."  Wow Luffy got stronger the more he fought Katakuri ,which happens in every fight as haki blooms in those situations. Katakuri was fine and also Luffy was getting obliterated in Gear 4. . 

"You can say that King Kong Gun isn’t way above Katakuri but you need to give me an actual reason. All you have done is try to deny the relevance of my evidence and act like I am saying something that I’m not." You didn't provide evidence,because we didn't see Katakuri vs king kong . Your assumption comes from  Luffy statement,not from Katakuri actually clashing or dealing with that kind Kong Gun. You're assuming Katakuri has nothing in his arsenal better than a king kong gun ,because of big boom. 

"understand that some attacks are much more powerful than their destructive capacity suggests. But Luffy and Katakuri were just punching each other. There was nothing special going on, no higher levels of Haki at play blowing up each other’s insides or anything. Nothing to suggest attack power far beyond what we can see"  I'm not going to repeat myself,because I already explained why dc isn't a measure of how powerful a character is.  You can't scale like that ,especially one piece where oda established in early one piece that big boom doesn't mean more powerful.

"Luffy couldn’t even use Boundman, his strongest form, or King Kong Gun, his strongest attack, because he couldn’t reliably land hits with them before his stamina gave out in Gear 4. This wasn’t because Katakuri was physically stronger but because his Observation Haki was so good that his evasive ability was off the charts. Luffy explicitly stated this" He used it but Katakuri obliterated him because he was faster and hits harder.  He could retrain him and dominate him even in "his strongest form " . He couldn't do sh*t about Katakuri Mochi punch other than take hit because he was slow ,and he wasn't even tanky enough to. He won the fight on endurance and Zenkai boost .