Hi GIGmatty,
Yes this makes sense. Thinner toppers will generally affect the “feel” and the comfort/pressure relief of a mattress and the primary or “deep” support in a mattress comes from the deeper layers in the mattress.
“Support” is often misunderstood because the goal of a “supportive” mattress is to keep the spine and joints in good alignment and this requires the type of contouring support that allows some parts of the body to sink in more (softer) and some parts of the body to sink in less (firmer) and this will vary on an individual basis. While it may be more than you want to know … there is more about primary or “deep” support and secondary or “surface” support and their relationship to firmness and pressure relief and the “roles” of different layers in a mattress in post #2 here and in post #4 here that may also be helpful in clarifying the difference between “support/alignment” and “comfort/pressure relief” and “feel” and how they interact together.
There is more information about some of the many factors or variables that can affect the price of a mattress relative to different manufacturers or retailers in post #14 here.
Phoenix