I have found that big tubeless tyres improve comfort a lot. (and grip).
But, there are some frames that a definitely more comfortable. Using the same set of wheels/tyres My Chumba is more comfortable than the P7 it replaced, but not as comfortable as a PACE 305 (but that was made of cheese). This comfort may be “compliance” in the frame, that’s how they were advertised anyway.
I’ve NEVER understood the whole idea of a more compliant frame, it’s always struck me as odd when the whole thing sits on tyres with air in them.
I remember reading reviews as a kid and bikes were slated (and presumably lost sales) for having a harsh back end etc. I just didn’t get it, still don’t.
I was sceptical too. The compliance in certain steel (and Ti and carbon) frames does not reduce the impact of bumps of any significant size but it does reduce the buzz from the smallest stuff. I swapped everything from a Boardman HT Pro to a Cotic Soul and the difference was obvious.
Frame compliance reduces the impact of high frequency low amplitude forces on your core mass, tyre compliance lower frequency higher amplitude, suspension even lower frequency even higher amplitude, arms and legs lowest frequency highest amplitude.