As a general statement, the closer to the hit the more important a component is. The tip, then the ferrule, then the shaft, the joint, on back. However, that is quickly proven false if something is really bad or really different. I had one bumper between two cues. One day I decided I just wouldn't bother swapping the bumper to the cue I was using. Much to my surprise, it was unplayable without a bumper!
I had my sister watching estate sales and such for cues since she frequents such things. Quickly discovered it was a bad idea but not before she purchased one of the under twenty buck Budweiser cue and case combinations for a few dollars. Sitting around my shop one day I got to feeling silly and went to work. I drilled out the butt as deeply as I could and cored it with a decent piece of maple. Put a nice three-eighth pin in the butt to match the quality insert going in the new shaft. Turned a nice shaft, nice ferrule, Moori II medium tip. Off to the local pub with a half-dozen tables. I wasn't known there but as soon as I laid the case on the table three or four kids crowded around to see my sneaky, so much for that! I had test hit the cue just out of curiosity so I had a baseline. Much to my disappointment, the cue still hit like caca! If I had to make a guess it had moved about halfway from pure crap to a decent, but not great, hitting cue. I think I would have had to fully core the butt and rewrap it to get it into moderately acceptable range. The butt was made out of a very soft wood like poplar. I think that would have killed the hit to a large extent no matter what changes I made.
On the other hand, many years ago I needed a shaft for my moochie on the fly. I went to a store that stocked a lot of Dufferin cues. Went through about twenty of them and selected the nicest shaft. I don't know what they thought when I gave it the ping test on the floor! They didn't say anything though. The butt was one piece wood. Stained maple I believe but this was in the late eighties or early nineties, too long ago to be positive. This butt played every bit as good as the moochie.
If we build a speed burner of a computer to play with and put one major bottleneck in the system, it isn't going to perform better than the bottleneck allows. The same is true of the pool cue, if it is a major bottleneck like that very soft poplar butt.
Hu