To a degree, yeah, but even in post production, there are a LOT of voices pitching in, voices that aren't necessarily the directors' first and foremost.
Lots of VFX are given a human touch that don't originate with the director, lots of sound design options, editing choices are sometimes decided on after an assistant has come up with an idea that another assistant likes that gets run up the chain til a director signs off, and then there's the score, which most directors don't really have the knowledge base to contribute to outside of basic "Make it sound more like x" direction.
"Auteur Theory" works a little better when you have a director doing like, 6 or 7 different jobs (Writer/Producer/Editor/DP/Director) but most directors don't do that.
Now, if we were talking modern-day television series, I could see an argument for Auteur Theory sticking a little bit harder, because showrunners are putting their thumbs on almost every decision even if their only credit is often "Executive Producer," but even those guys admit that what makes their product so great is the collaborative nature of the filmmaking.