base2 

The engineering merits of the double triangle diamond frame leaves little room for "vertical compliance." Lateral and tortional stiffness, however is another matter.

Titanium is very strong. It is also very springy. If a titanium frame were designed only as strong as necessary and only where necessary like a carbon frame tends to be designed, it would be so noodley so as to be dangerous. Consequently, all the supposed weight savings is eaten up by additional material added to address the absence of tortional and lateral stiffness. The end goal/result is often a ride comparable to a steel bike with some weight savings but not as much as *could* be. The trade-off is often cracking sometime far along the life cycle as manufacturing can be difficult to execute and the elasticity of the welds is different than the tube that was welded. (On a general level.)

Carbon, on the other hand, is not so "springy" and it can be very light weight with enough strength to do the job. So, there is a lot of freedom to design around an intended use. Larger diameter down tubes, head tubes, larger bottom bracket areas and thicker chainstays can be done with very little weight penalty. (Conspicuously absent from this tube growth phenomonon is top tubes and seat tubes.)

For "vertical compliance" ie "comfort" in the traditional sense, tires (bigger softer "air springs") and seatpost will yield much more fruit. A longer seat post will offer much more deflection than a short one. You can see this in the recent trend of lower and lower seatpost collars and ever more sloping top tubes in more recent designs.

I think that what a lot of people mean when they repeat: "Steel is real" (& by extension, titanium) is that the frame twists, the quill stem flexes, the side of the handlebar that had weight on it flexed, the bottom bracket deflected, etc...All give the impression of a smoother ride. Whereas a carbon frame by nature of desing is intended to resist those forces so can be perceived as "wooden" by comparison.

Designing flex into a carbon bike has been the latest trend with IsoSpeed, IsoShock, Zertz, decoupled seatposts, etc...

All that is to say, the smaller frame will be smoother not because it is Titanium, but because all the bits that stick out will have room to be flexier.