I may be the oddball here, but that 3 second duration does not comfort me. The only time I would notice it is if I am sitting in front of the computer. While someone snapping a photo of me while working is disconcerting, it is not the end of the world. Someone snapping photos while I am away from the screen is more troublesome. (Or it would be if my computer was facing an open space, which it doesn't.)
[1] https://www.businessinsider.com/lenovo-thinkshutter-laptops-...
The exploit mitigations to prevent you from getting an initial foothold.
The sandboxing preventing you from going from a low-privileged to a privileged process.
The permissions model preventing unauthorized camera access in the first place.
The kernel hardening to stop you from poking at the co-processor registers.
etc. etc.
If all those things have failed, the last thing to at least give you a chance of noticing the compromise, that's that LED. And that's why it stays on for 3 seconds, all to increase the chances of you noticing something is off. But things had to have gone pretty sideways before that particular hail-mary kicks in.
And, of course, covers are an option.