Progress is a misunderstanding here.
Of course complex multi-cell organisims could only evolve after a certain time passed,
but there are still many "primitive" single-cell organisms,
in constant evolution.

Its just that the variation-space and chance for variation
increases with time.
This can also mean a loop back to previous adaptions.

Take wales/seals for example.
They evolved from maritime creatures to land creatures,
back to maritime creatures.

Ants evolved from primitive crawling insects to flying wasps back
to crawling insects.

We just see many "higher" creatures, because there was
a valid time for them to have a chance to evolve.
This must not make them better adapted than primitive single-cell
organisms in the long run.


So there is no intrinsic direction, just a higher chance for
manifold variation given time.
Complexity survives as long as less complexity is not better
adapted or could push out complex organisms.