Agree about Joshua that he is the better 'athlete' and it has never been a secret that the talent pool is deeper in boxing than in kickboxing and mma because of many reasons. At the end of the day TBH I don't care that much about athleticism. This is our combat sports world. We can't force kids like Lebron James or Usain Bolt to do muay thai or MMA. These sports are for tough men not athletic men. Boxing and MMA legends grow from poverty and passion after all. In school it was the same, the strongest and most handsome guys sucked at fighting or to better put it: didn't like getting punched in the face
Obviously athleticism is not the be all and end all of fighting, and there are numerous examples (even in boxing) of elite fighters that are not particularly athletic.
But you can't overlook how important athleticism is and how far it can take you.
Look at Roy Jones. He was an insane athlete, with unreal speed for his size, and agility and power. Yet he was not the craftiest or toughest or most well schooled boxer, and when his athleticism faded, his overall fighting ability nosedived.
Contrast that with Hopkins and Floyd who relied more on skill and craft than athleticism, and as such managed to still be top tier elite fighters when their athleticism waned.
Pacquiao is another example of a guy who became an elite fighter mainly through athleticism, having an unbelievable combination of speed, power, agility, workrate, and stamina. So much so it just overwhelmed people - even more experienced, better schooled boxers like Barrera, and of course much bigger guys when he moved up in weight.
Unlike Roy, Pacquiao did gradually become way more crafty and skilled though, and even when he slowed down, was still boxing the shit out of solid fighters like Bradley.