They spot you if you're exposed. Hide and you're good.
There is a mechanic to show you visibility to enemies, just find the right hack
You can Zoom in/out with the scanner. You can't if you're scanning but move it a bit upwards (to the sky for example) and suddenly you can zoom.
So, no it's not disappointing as hundreds of other things people are reporting (because it's cool to hate on the game?) - you just have to read more and I guess.. play better.
I’d have to agree with you on that front. I remember that I had to assassinate an Animal who ran a fight club in Santo Domingo (it was also a location for a Beat on the Brat fight). And let me tell you this: Those gonks might be juiced up on horse growth hormones and who knows how many steroids, but they’re as eagle-eyed as... well, an eagle. But with a little analysis of their patrol patterns, a quick Distraction hack, and a whole lot of Lady Luck on my shoulder, I not only managed to flatline the Animal, but I managed to escape through the front door while his body was still warm. At times, the stealth can seen to be too easy (I was playing on Normal difficulty), but it can still be very satisfying when you manage to pull off a theft or a Search and Rescue without anyone being aware that you were even there.
It is possible to not get detected at all during the mission, apart from the obvious cutscene when you get detected anyway, but in the end it makes no difference, as exfil cutscene is guns blazing anyway.