Trouble is you can't read the articles without giving them an email address... no thanks! LOL!
My take for my dogs...
Havanese are small dogs with low body mass and although they do have an undercoat, it is not thick or protective. Nor do they have a harsh, protective outer coat. If it's wet, they suck up water like a sponge. If it's cold but DRY and it's not windy, mine do fine outside for short periods of time, like for pottying without coats. They will even play in those conditions and are good at self-limiting.
If it's very wet or windy, or if we are going for a walk, when they will be out in the elements for longer, they get coats. Lighter coats if it's not too cold, if it's below freezing, they get puffy coats. Above 40 and sunny they go nekkid.
Oh, and Kodi wears a puffy in his crate in the car in the winter. It takes a while for the heat to get back there, and in his puppy cut and at his age, he definitely get chilly sitting still back there. Panda doesn't seem to, but she has a lot more coat. Pixel's crate is a RuffTuff Kennel, and much more enclosed. It traps heat better and is also in the middle seat. I throw a blanket over hers and she stays toasty.