Besides, the vast majority of users will not be under active attack. Having an on-screen popup when you try to use the webcam telling you that it has been hardware-disabled is quite a must-have. If you don't have something like this, you'll get a lot of support calls which boil down to "you accidentally pressed the kill switch, press it again to re-enable".
For example, when you are "required" [1] to run surveillance software on your computer.
[1] https://www.vice.com/en/article/n7wxvd/students-are-rebellin...
How well would tape work on that?
Yep. This was an extremely common issue in the mid-2000s, when laptops started integrating wireless hardware with hard power switches, often on the side of the laptop where they could easily be toggled by accident.
It's basically a false sense of security which is generally worse than doing nothing.
Detecting the pattern in a prng stream is equivalent to finding its Kolmogorov complexity. https://en.m.wikipedia.org/wiki/Kolmogorov_complexity#Chaiti...
This assumes an attacker is targeting you specifically since otherwise this is all moot (a broad attack could care less as to why your microphone is off).
Really, though, in general there's just no point to this altogether; just cutting power/data to the mic is fine. There's no need to attempt to fool someone with fake audio, outside of some very edge-case scenarios that I'm sure Dell (rightly) does not care about.
And the spy device/software knowing the user has "switched off the means" vs "they are broken" is important because?
What exactly do you expect that to accomplish. Anyone actively targeting you getting literally NO SOUND OR VIDEO is going to know that you've flipped the switch just the same.
Even the quietest apartment has HVAC that will be picked up. If they're recording for hours they're going to hear people walking by. The camera itself will still provide an image, even if it's black, that looks different than no signal at all.
If a nation state is able to get to your laptop they're going to figure out pretty quickly that you're "feeding something pre-recorded" into the mic and camera every time you have a meeting. Ignoring the insane effort you'd have to put out to feed that in and make it even semi-believable. For starters they are presumably tracking who you're meeting with - are you going to have a meeting before your meeting to pre-record? Hope they don't figure out that you're saying the exact same thing in two different meetings? Somehow have root on your laptop but aren't bright enough to figure out you're feeding data from a local file into your mic and camera?
If you have a spy device connected to your computer or have malware running, you are very screwed in a million different ways already. Limiting knowledge of hardware state to malware doesn't buy you much.