I'm not so sure about this - I admit I haven't used the lens before but my impression was always that the overlapping range was comparable with the 18-135 having a slight edge. At the long end the 18-135 is soft.
Pentax SMC-DA 18-135mm f/3.5-5.6 ED AL [IF] WR - Review / Lens Test - Analysis
Pentax SMC DA 18-55mm f/3.5-5.6 AL WR - Lab Test / Review - Analysis
I do agree that the 18-135 has better build quality and is probably easier to unload (that is, if you intend to unload later on). Anyways, the 50-200 doesn't have immaculate IQ either (being a kit lens), but is reasonable enough, and has a slight edge over the 18-135's longer focal lengths, especially when it comes to corner performance.
Pentax SMC-DA 50-200mm f/4-5.6 ED - Review / Test Report - Analysis
I guess another factor that you would want to consider is if you actually wish to avoid changing lenses a lot. The 18-135 would have most of your commonly used focal lengths covered. The 18-55 can be a bit short sometimes when it comes to shooting pets.