Hi calentarse,
I split your post into a new topic of its own because your questions were starting to drift outside the scope of the original topic you posted in.
Yes … more pressure relief would “translate” into being a little bit softer. For some people it may be beneficial, for some it may be detrimental, and for some it may be more “neutral” but as you mentioned the only way to know whether it would be better or worse for any specific person would be based on your own personal experience when you sleep on it.
These are all very different mattresses that have different designs and combinations of materials and would all have a different “feel” and response even in the same firmness level. The Tuft & Needle has a high performance polyfoam comfort layer on top of a polyfoam base layer, The Casper has a synthetic latex layer on top of a memory foam layer on top of a polyfoam base layer, and the Dreamfoam Ultimate Dreams Aria has two memory foam layers on top of a polyfoam base layer.
There are also no “standard” definitions or consensus of opinions for firmness ratings in the industry and different manufacturers can rate their mattresses very differently than others so a mattress that one manufacturer rates as being a specific firmness could be rated very differently by another manufacturer. Different people can also have very different perceptions of firmness and softness compared to others as well and a mattress that feels firm for one person can feel like “medium” for someone else or even “soft” for someone else (or vice versa) depending on their body type, sleeping style, physiology, their frame of reference based on what they are used to, and their individual sensitivity and perceptions. There are also different types of firmness and softness that different people may be sensitive to that can affect how they “rate” a mattress as well (see post #15 here) so different people can also have very different opinions on how two mattresses compare in terms of firmness. This is all relative and very subjective and is as much an art as a science.
The Dreamfoam mattress that would be the closest to the Tuft & Needle in terms of the type and quality of the materials inside it would be the Arctic Dreams mattress (see this topic) which uses very similar materials and has a similar design to the Tuft & Needle but I don’t know how it would compare for you in terms of firmness.
When you can’t test a mattress in person then the most reliable source of guidance is always a more detailed phone conversation with a knowledgeable and experienced retailer or manufacturer that has your best interests at heart and who can help “talk you through” the specifics of their mattresses and the properties and “feel” of the materials they are using (fast or slow response, resilience, firmness etc) and the options they have available that may be the best “match” for you based on the information you provide them, any local testing you have done or mattresses you have slept on and liked or other mattresses you are considering that they are familiar with, and the “averages” of other customers that are similar to you. They will know more about “matching” their specific mattress designs and firmness levels to different body types, sleeping positions, and preferences (or to other mattresses that they are familiar with) than anyone else.
A good online retailer or manufacturer will generally make suggestions that they honestly believe have the best chance of success based on the information you provide them when you talk to them on the phone because this is in both your own and their best interests but once again … at the end of the day the only way to know for certain whether any specific mattress is a good match for you in terms of comfort, firmness, and PPP (or how it compares for you to another mattress that you have tried) will be based on your own careful testing and/or your own personal experience so if you can’t test a specific mattress in person then the options you have available after a purchase to either exchange the mattress (or individual layers or components in some cases) or return the mattress for a refund (and any costs involved) would generally become a more important part of most people’s personal value equation just in case a mattress you purchase doesn’t turn out as well as you hoped for.
Phoenix