I think that many guys, especially those starting out, neglect boxing skill and favor conditioning exercises. I think that this goes on among pro level athletes as well. Probably because it is easier and less repetitious and boring.
It does a serious disservice to fighters, though, and not just in the obvious neglect of skills. A lot of physical conditioning becomes very mindless and repititious, and, even when it isn't, you aren't thinking boxing. So you gets guys like Troy Dorsey; super fit but stupid as a puppy when it comes to boxing. That is why cross training is wasted time; boxing is a mental exercise.
So teach your brain. Instead of jumping rope, shadow box extra rounds. There is an old saying: The strong take from the weak while the smart take from the strong.