You offered,
"The problem I have with that belief is that it must posit that death was a fact of life for millions of eons before death was introduced into the Genesis creation account solely as the result of Adam's sin in the garden." Eden may not be so long ago as eons, since the Eden story relates the advent of the spirit injected or breathed into the human soul.
"If death is the inevitable result of sin ... uncountable quadrillions of 'upwardly mobile' animals who must have lived and died prior to Adam's entrance into the creation account must of necessity have been capable of consciously sinning against their Creator ..." If these animals had no spirit they could not sin against the spirit of God; remember, the death spoken of is a spiritual death not a physical death.
"If God is not a perfectly just and unchangeable Creator, as the bible claims him to be, the entire biblical plan of salvation and the scriptural explanation of the absolute need for an infinitely capable and perfectly sinless Savior who died a substitutionary death in order to atone for man's sin falls apart at the seams." How do you reason this out when you take the death to be a spiritual death and calculate those lives not in the human family since Adam to be without a spirit component in their soul of life? The scriptures say that 'all of creation groans' since the fall of Adam effected even the animals and is corrected by the Grace in Christ Jesus. The scriptures do not include all the uncounted living things prior to Adam, rather the Bible starts the fall and redemption with the saga of Adam.
And finally, God's economy is very different from our human understanding. Without a more thorough understanding of what the universe is, we are floundering with partial theories about God's calculus. Perhaps that's why Physicists/Cosmologists are busy revealing more about the nature of this amazing universe.
I'm not sure that I understand all that your reply says regarding my comments and those of ClancyJ. It's very late here and I have had a very busy Lord's day, (not the intended purpose for the day I admit) so please bear with this tired old brain until I can study your comments on my comments with a clearer mind. I think I can agree with most of your comments on my comments, but I don't want to commit myself to that without another and more careful reading.