The only identified issue with film caps is a potential for mechanical resonance specific to a frequency but audiophiles make up all kinds of things like posts in this thread. Caps can be in high or low pass filter networks. They are critical in both.
So which is it then? Because if they are so critical then it would seem we would want the best ones, and you already admitted there are problems like mechanical resonance. Which is indeed a factor. So how can you be sure we are just "making up all kinds of things" about which is best? Help me understand your, uh, reasoning.