Time Dilation as an explaination for the expansion of the univers acceleration

To come with the theory of an accelerating expansion of the universe scientist compared the redshift of galaxies at different distance and noticed that closer the distant galaxy was faster it was going away from us.

If the universe is expending that also means that in the past the universe was denser, according to my understanding of GTR time was slower then it is now.

It means that as the universe is expanding the time should accelerate.
An object moving at a constant speed but in a time frame that is accelerating should be observed as accelerating (even if speeds remains constant in its own time frame).

If all odf this is correct a universe that is in expanding at a constant speed should be observed as accelerating.

My question is :
Why this cannot explain the "observed" acceleration ?