The radio must be faulty. You should have it looked at or replaced by Apple. They are best in class or at least better than mid-ranged laptops, if you’re only comparing to specialty PC hardware.
I have used a few, and the other most recent one- a MacBook air- had the exact same issue. I wouldn't call anything I use specialty hardware, though both the go spectre and surface book 2 were, at the very least, on the high end of midrange. The Dell xps I honestly don't have much good at all to say about.
Or an aftermarket sticker is interfering with the wifi antenna?
I definitely do not put any stickers on my laptops, and especially not ones that are not owned by me (i.e. company issued, which are the only macs I will use).
Is that a real issue? A sticker is enough to impact a wifi antenna enough that people would notice?
I'm not sure about the impact being noticed. I thought the wifi antenna hid behind the Apple logo on some machines, but I don't remember which machines.