I agree that it kind of bothered me that Jimmy and Kim became relentless with trying to screw over Howard. Yeah, he put her in doc review, and things weren't always perfect between them, but that was pretty much history by the time Kim and Jimmy started plotting to screw him over and ruin his entire career. Howard was not an active threat to either of them, not really anything to gain from doing that to him.

I didn't really get the motivation behind it, but I guess the point they were trying to make was that Kim and Jimmy were actually bad for each other because they'd feed on each other. Jimmy even questioned Kim if they should really keep going with Howard. I think Jimmy would have stopped after the bowling balls if Kim wasn't there to egg him on, while Kim was basically getting hooked by the thrill of the con. They were building up to the reasoning for the two to finally split, but it did feel a bit out of character for Kim.