JU88 was never intended to replace the Ju 87 Stuka.
The JU88 was a medium fast level bomber with capebility of dive bombing. Stuka was a 100% dive bombing airplane ment to take out tanks and infantary (and similair), Stuka was one of the few planes capeble of dive bombing in 90 degree angles aswell.
Nothing to do with eachother.
Give us our Stuka!