I also have a deflection issue with my McDermott, but for $140, I knew I wasn't getting a top of the line cue. But it was mostly for bar leagues. And it still hits far better than the Viking that I paid nearly 3x that for.
Once my custom is ready, I'll probably have the cuemaker make me a shaft for the McDermott (my custom also has a 3/8" x 10 joint). Not only do these shafts tend to deflect, but I've also got some slight warpage in it already, and I haven't even had it a year yet.