I do own an RC-64II that I bought it along with my RF-7 II speakers, but I decided to use my RF-7 II in 2-channel music only rather than for my home theater, so the RC-64II is still boxed up. For my home theater, I am happy with the RP-280F L/R + RP-450C center channel so far.
I think if you ask the Klipsch designers they will probably agree with my conjecture that the RC-64 is optimized for speech while the main RF-7 II/III is probably not.
However, I generally agree with your statements in most cases, EXCEPT that the discussion at hand is in reference to the RF-7 II setup. My personal experience with the RF-7II is that it sounds lacking in the mid-range, including the human voice range. That's why I think the RC-64 II will be a better option in a home theater application since it's presumably optimized for speech.
By the way, I also have a pair of 1970-era La Scala. I may move the La Scala into my theater room because I like the rich sound, especially in the mid range.
It's not entirely correct to project your positive experience with a three-speaker La Scala setup onto the RF line to conclude the same positive result would be produced with the RF-7 II. The La Scala and the RF-7 II have different frequency response characteristics relative to all-important vocal mid-range frequencies. The La Scala sounds very rich and mellow in the midrange but the RF-7 II does not (at least not without some serious equalization).