The PT is proof that directing actors is just as important as everything else.
It is important but not nearly as important as the elements I mentioned. There are plenty of films that have rather average acting but are great because of the idea/story/screenplay (for example Terminator and Predator).
There are movies where the reverse is true.
I honestly couldn’t think of any but I would like to hear your examples. I my opinion great acting alone just cannot make a film, with average idea/story/screenplay, great. While there are countless more examples I can give for the reverse case.