Originally Posted by
WhyFi
You'd lose pretty heavily. There are no elastomers in the Domane frame. IsoSpeed is essentially pivot points that give the Domane a very long seatpost and a very long steerer. They do an incredible job of deflecting the brunt of the hits. Also, as I stated previously, my Domane with 30mm tires at 65/70psi (front/rear) is more comfortable, in terms of taking the jolt out of bumps/cracks/potholes, than my gravel bike with 38mm tires at ~40psi.
Again, I'm not arguing against tire compliance, just saying that it's false to say that any ol' road bike with 28s will get you the same kind of compliance as a Domane (and potentially a Roubaix, but I have no experience there).
Others have different experience, and I would tend to believe them - the amount of compliance available in 'decoupled' frames is still miniscule compared to the suspension available in properly inflated 40 mm tires. Methinks you may be discounting other factors that change between the bikes, or experiencing bias confirmation when interpreting the results of your comparison.