Show me where is it not. I fail to see the direct link. You've said there are parallels that may be observed. Not one to quibble, let's give you that.
The conclusion you draw, that evolution in nature demands that dispensationalism must be true, is what I challenge. It's that statement that gives me pause. Do you really want to assert this? I understand that you're actually trying to argue the inverse, but because primary relationship does not exist the inverse can not be asserted either. Your reasoning is convoluted, that's what I'm pointing out, or at least, trying to.
Let's get back to what the Word of God says:
1 Corinthians 15:46 However, the spiritual is not first, but the natural; then the spiritual.
OK, I will try and be clear. To understand what is spiritual, we have to understand the natural things in the world. It is of no wonder why throughout the Word imagery of nature, water, birds, trees, vines, wheat, tares, weeds, etc point to the deeper truth. What is embedded in the physical, points to the spiritual matters we cannot see.
Romans 1:20 For since the creation of the world His invisible attributes, His eternal power and divine nature, have been clearly seen, being understood through what has been made, so that they are without excuse.
What I am pointing to is nothing in the natural world, points to what dispy says is a new wineskin that is to usher in the age of "grace". Instead of trying to imagine evolution and dispy teaching as being in a box and the two pieces must match up perfectly to make my argument, think of what the function is of each. Evolution teaches an upward progression of primitive man eventually making way for 20th century man, dispy does the same thing with man now being an evolved, NT believer. Dispensationalism teaches that before Christ, believers were devoid of the church, grace, apostles, Holy Spirit, new birth, salvation by faith, baptism, tongues, healing, etc. The bible teaches otherwise though.
So if we go back to the natural aspect, if 1 Corinthians 15:46 is true and IF dispy lines up with this passage, and many other passages about the world and nature in the bible, then our natural world would have likewise improved or must now be more refined. But that is false, the same giraffes that produced the same giraffes have not changed in the last 2000 years. Abraham produced the same fruit as any other believer today. If anything, we are in a state of entropy and have continued that way since the fall of Adam and Eve (Isaiah 51:6; Hebrews 1:10-11).