TrackSmart

First, as a CAAD10 owner I agree with your take on the lively and fun character of these bikes. They feel fast and make you want to ride fast. I also think the feedback you get from the road is helpful (i.e. not so muted that you can't understand the character of the road and the limits of your potential traction). It's kind of like the difference between a car with good road feel versus a car that prioritizes soft, squishy comfort, though obviously to a much lesser degree given we are talking about rigid bike frames here with very little real-world vertical travel!

My only full-carbon bike was a replacement for an aluminum frame I damaged in a crash. This is a gravel bike (Niner RLT9 --> Bombtrack Hook EXT-C frameset) and for rough-and-tumble dirt and gravel roads I do notice a more "muted" ride characteristic on the new frame. All of the same parts went from the RLT9 to the Bombtrack frameset, so it's a good comparison of apples-to-apples. I honestly didn't think I'd be able to tell any difference in terms of ride quality (similar geometries and big-fat-38mm tires at low pressure), but the carbon frameset was different. But not dramatically different. Both bikes were comfortable and highly enjoyable. And the 0.8 lbs weight savings of the full-carbon frameset (vs aluminum frame and carbon fork) and supposed compliance hasn't changed my ride speeds to any measurable degree. But yeah, the carbon bike has a slightly more muted ("smoother"?) ride quality. I can't say whether that's "better" or not (strictly personal preference).

Overall, I do think that for unsuspended bicycles (i.e. with rigid frames) people attribute more supposed "ride comfort" to rigid bike frames than is warranted given how little modern frames flex vertically under load compared to tires and seatposts (of the modern carbon variety). There are hard numbers to back this up (i.e. how much potential flex happens in different parts of the bike). I suspect that even modern carbon forks and handlebars, while providing fairly small amounts of compliance, probably provide more vertical damping than the frame of a rigid bike. So it's likely that going up one tire size (at lower pressures) would have a similar influence on ride comfort than the difference between a solid "mid-range" frame and a really expensive "high-end" frame if both were well-designed.

Finally: I think the complete "package" of a bike and its parts causes a large enough amount of variation in ride feel that it can be hard to attribute differences to the frameset (by itself) unless you are in an unusual situation where everything else on the bike is identical. I was in such an unusual situation and the differences, while noticeable, were subtle (that is to say they were far from night-and-day). Now, in my case, I had a mid-range aluminum frame (that was criticized by reviewers as being "harsh") and upgraded to a mid-range carbon frame (that reviewers said was very compliant). Despite those supposedly large differences, we are talking about subtle shades of difference in the real world if we keep everything else similar (e.g. components and geometry). I think we are talking about connoisseur differences, rather than major comfort and performance-enhancing levels of difference among decent quality framesets (whether mid-range or high end). That's my take from the closest thing to a controlled experiment that I have!

EDIT: All of this presupposes rigid framesets. I realize that some modern road frames have various forms of micro-suspension in either the seattube area or headset area that likely make a bigger difference in compliance. I don't personally want anything that complicated on my own road framesets, but again, that's personal preference.