To make general characterizations of how any frame material rides, that can be supported by statistically significant data, is rare and difficult. The claimed benefits of a Spec Roubaix (I don't own one nor have I tested one) are comfort with performance. It's hard to generalize that all carbon frames will deliver comfort with performance. If one or even a few carbon models are not reliable, that says nothing about the set of all carbon bikes. Similarly for steel and aluminum, or anything else. It's possible to engineer or build any frame badly. Probably less likely with steel due to the depth of industry experience, however.
I'm less interested in C because few of my stashed parts will work, for the most part. It's also hard to fine one that will take wider wheels, fenders, and racks; which are options I want. But if a Spec Roubaix arrived on my doorstep, I'd ride it.