Making banket statements fai to take into account variables. Type of grass (Poa, Bent, Fescue (or any combination thereof) and different strains of Bermudas. Subsoil makeup - Perched water table USGA, California, push-up with 4-6" of sand topdressing. Mowing Regime - walk or tri-plex mowed, mowing frequency, single or doube-cut, cut and rolled, rolled on non-cut days. Irrigation - totaly automatic, weatherstation/sensor controlled, sprinker syringed vs hand watered. Wind, Sunlight/shade, Trees (tree roots), and canopy temperatures can a play into how firm or soft a green is. One aspect that has gotten no talk here is that of the amount of Thatch that is present. A green can be relativey dry but have a thick thatch layer which will cause it to be soft. I have seen this with Poa greens that were maintained at double-digit speeds but easiy marked. I think top-dressing plays a role in this.
Actually, for many club members, this is the best of both worlds - fast but soft- because it is harder for them to hold shots on firm greens. But just because they are soft, it doesn't mean that they are wet.
I just saw a survey from England on golfers desires and #1 was True putts not Fast putts. Perhaps in the quest for Truer greens, they were rolled more, cut shorter to mitigate the effects of grain and topdressed more frequently to remove minor surface varients. All these tactics also lead to faster greens. And since speed is easiy to quantify, it becomes the defacto measuring tool.