I think who vs. whom really doesn’t matter anymore, though I’m sure that at one time it did. All it’s good for now is discussions like this one.
Using “whom” does often sound pretentious, and those who say that it doesn’t are simply the ones who don’t mind if they sound pretentious. (This doesn’t mean they are, just that they might occasionally sound like it.)
In my opinion, “whom” is no longer useful, no longer worth defending, and best avoided in all situations - including the most formal ones. Just my opinion, and I respect other opinions.