Still got my full sus 1964 Moulton and this Dahon:
A small wheel bike can fairly fly along on a rough road with suspension, but they tend to pitch a bit under hard pedalling. The long wheelbase on the original Moultons helped avoid this.
I think suspension is redundant for large wheels on the road,. Grab a 29er ad use tyres like the 2.35″ Big Apples I’m using on my Scandal:
If you use back roads a lot, the Big Apples will swallow up almost anything and you don’t have the penalty of carrying all the weight of suspension, or any pedal bob.
I don’t know how people who ride for speed would get on with them, but it makes putting a 100 mile day in dead easy, or at least comfortable.