Okay, first up? NVGs ruin stealth camo, especially lvl-3 ones, they work just as well in a morning map than in a night one, and allow you to easily detect any enemy in your field of view, but the tradeoff is that in order to be able to effectively use them in both types of maps, you need to give up three of your four slots to use it, and that's a lot of slots, trust me, secondly, stealth camo isn't that good in the first place, it's a trade off for you being able to stay stealthed while, you still have this weird glassy texture to you so if you start moving too fast in plain sight, you are gonna get spotted, it's as simple as that.
And unfortunately, I have been that guy that has killed a tranqued enemy, but they don't do it for their K/D ratio, hell, I don't know if MGO even records that, they do it because they're kinda in the heat of the moment and they see a bad guy crawling around and, well... You know the rest.
And buddy spawns are fine, well, not fine, but still alright, because they're incredibly noticable, red fire and a stationsry outline of the character for, like, three seconds? That should give you plenty of time to prepare.