Some of what you are seeing in price difference is the cost to lay-up the frames; materials in the lay-up, the level of precision in the lay-up, which is a hand-done process in the mold and the engineering that goes into the lay-up itself.
As I type this there are three men from one of our (Felt) factories and one of our managers reviewing lay-ups in another room. I'm writing a technical article about new proprietary lay-up additives we're using on one bike now and several more soon.
There are no "bad" lay-ups, but some are much more elegant than others. They are lighter weight, stiffer and more compliant vertically. Simply greater attention to detail as the carbon fiber is placed by hand into the molds and better quality materials. You get what you pay for.
I work for Felt, so obviously I'm not objective. I can tell you our lay-ups are done by hand by skilled craftspeople, some of them third generation, who are meticulous and exacting at placing the carbon into the molds. Our materials engineers look for materials that bring high-end ride to value priced bikes, and out lay-ups are designed by them with that agenda.
One advantage we have over the two brands you mention is the technology that presses carbon composite lay-ups to the outside of the mold during the molding process. Several brands use this process, so it isn't unique to use, but it is generally only used at the $5K+ price point. We use this manufacturing and molding technique well below that price point.
Ultimately, each of the three brands you mention have "earned their stripes". Quintana Roo invented the triathlon bicycle. Kestrel invented the aerodynamic carbon fiber molded bicycle at the manufacturer/retail level.
Consider your ownership experience, level of dealer support (a key concern) and the other factors that will influence your ownership experience. That may help you make a decision. FWIW, to toot our own horn (what I'm paid to do), we have a much larger dealer network ready to provide support than either of the other brands you mentioned, if that is a factor to you.