I'm torn on this. On the one hand, boxers don't really have that many tools in their toolkit, but they do pretty darn good with them. Take someone who's done boxing for ten years, and I guarantee you they've got about this many reps on each of their jab, cross, hooks, and uppercuts. And I don't think there's much more than that.
On the other hand, the concept of resistance training comes up...but how do you provide resistance training if you do not know how someone else would resist? For example, if I go to a boxing gym and practice for 10 years, I'll know how to respond to any dodge, duck, dip, dive, or dodge. But I'll be completely clueless when they counter with a push kick or by grabbing my arm, because I won't have been prepared for that counter.
Now, I could be wrong (I haven't actually trained boxing, just using it as an example). But if you're going to practice for resistance, then those you're practicing with must be able to adequately provide that.