I wonder if there were multiple generations of Devil Fruits? So, Monet's Snow Fruit was the precursor to Aokiji's Fruit, Ace's Fruit was the precursor to Akainu's Fruit, the Ball Fruit is a precursor to Buggy's Fruit.
The Toshi Toshi no Mi is the inferior version of the Toki Toki no Mi, the same way the original Pacifista are weaker than the Mark III//Seraphim.
So, we'd have Zoans come first, then Paramecia, then Logia, which is why Vegapunk can create artificial Zoans, but not Paramecia without the green blood, and can't make Artifical Logia Fruits.
I'm still trying to figure out who will get Toki's Fruit. Ohhhhhhhhh, wait, it should be Hiyori.