Blasphemy perhaps but I don't think he looks good in that shirt at all. Too baggy about the waist and WAY too baggy about the arms.
I agree completely. Sure the equation becomes tautological with McQueen owing to his uber coolness - to wit, what he wears is cool, because, well, he's wearing it.
But that shirt looks too big on him. At the time (and when I was growing up in the '70s/'80s), that was the only option for thin guys, so you kinda got used to the look - but it was far from ideal.
Now, here he is in some clothes tailored to really fit him - not skinny, just slim cut for a slim athletic frame (all from the movie "Bullitt"):
The turtleneck and sport coat are, IMHO, tailored perfectly for his frame. They are not blousey or billowing or tight or skinny - just well tailored and in proportion to his frame.
In the mirror reflection, we see Jacqueline Bisset wearing one of McQueen's shirts that is too long on her.