Hi jfmugen,
Yes. The density of foam is the biggest factor in its durability but any density can be made in a wide range of softness/firmness levels.
This would depend on whether you are talking about “pressure relief” firmness or “support firmness” because there are different types of softness and firmness (see post #15 here). The F/M/S layering would have the firmest “feel” or “pressure relief” firmness but the support layers would be on the softer side. They also have some examples of different arrangements in the description here which may be helpful. I don’t have any personal experience with the mattress so I don’t know how any of the arrangements would feel for me (much less how it would feel for someone else) and people with different body types, sleeping positions, or sensitivities may have a very different experience or describe the same arrangement very differently. The F/S/M would be a little softer as far as pressure relief and a little firmer in terms of support.
Foam in the deeper layers will compress less than the same foam in the upper layers of a mattress because some of the pressure would be absorbed by the layers above it so a softer layer on the bottom of a mattress will compress less and likely be more durable than the same layer on top of a mattress. Firmness/softness is a secondary durability factor and there is also more in post #4 here about the many variables that can affect the durability and useful life of a mattress relative to different people.
In most cases I think that most people would use the soft as one of the top two layers but probably not on the bottom.
Even if you did know the ILD’s of all the layers in each mattress the softness/firmness of a mattress depends on other factors as well (see post #4 here). I really don’t know how they would compare in terms of “feel” but the top layers of the Tuft & Needle would be softer than the support layers and probably softer than the firmer layers in the 12 in 1 as well.
Phoenix