The activation barriers sure feel artifical sometimes, but we are dealing here with compromises. The system TFP uses for its POIs needs few CPU cycles and that is surely why TFP uses it. I hope they will eventually use optimization wins for more zombies instead of more natural senses of zombies, but your mileage may vary.
Yes, anything that lowers immersion is a potential problem. 7D2D will be released with lots of problems still in the game because compromises have to be made. The only question is which problems TFP will fix and which it will keep because they just don't have the CPU budget to fix them.
Someone checked the xmls and found that the automatic activation happens in much less than 10% of rooms, I think it was even below 5% but I'm not sure. There was just one building which overdid it with almost every room having automatic activation and I made a bug report about it.
That is why I think the issue gets overblown, because if it happens in every 20th room then it means stealth works in all the other 19 of 20 rooms as expected and the 20th room is an interesting variety stealthers have to be prepared for.
And it is possible to restealth and there are other ways to prepare yourself for such situations. It makes stealth a lot more interesting for me because everyone can play stealth, but there is a way to improve your stealth play further and master it.
So you don't use stealth but have a strong opinion about it? Well, I do use stealth and like stealth play. Maybe that is the difference

. I also like the occasional surprise and other players may not like surprises.
As long as stealth isn't 100% effective I'm good, so a change like the one hiemfire talked about would be fine. But I'm ok with it as it is as well.