thoft - Jim's MO was to design each model to its full potential. In the case of small speakers, the trade-off was how deep the bass goes. Yours are about 50Hz anechoic, possibly deeper in your room. The PCS gets a big boost by having the 4" midrange to fill the mid frequencies both on and off axis, while not adding the expense of another crossover circuit - that’s significant.
The PCS debuted in 2000 using the first generation coax developed for 1998’s CS2.3. The PCS sold about 2000 pair, at the low end for a Thiel model.
I heard that Jim was working on a CS7.3 in which he hoped to develop a next-generation coax using the RadialWave or StarPlane diaphragm with a next-gen mechanical coupling and rare earth motor like the CS2.3 and 2.4. That driver could have a smaller, lower mass midrange diaphragm than the 3.7 which has to interface with a 10" woofer. That new coax would have been used in his 2.7 and PCS2. After Jim's death Thiel Audio had developed a StarPlane CS1.7 woofer, which would have been upsized from 6.5" to 8" for the CS2 series.
In New Thiel’s (2013) first year with Steve DeFuria and Bob Brown onboard, they started working on these drivers, but found it beyond their depth to bring the designs to light.