I use an Outdoor Research Helium bivy for cold, windy hikes. It has a low, wind shedding profile. Inside the bivy I use a high R factor sleep pad and a 0F sleeping bag, plus wool base layer.
The bothy bag is for day hikes in parts of windy Britain.
The bothy bag isn’t a tent, but a hiker or two can put it over their head to get out of the Windchill or a rain, and boil up a tea or lunch.