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.