While I was joking, of course, France’s economy actually was quite a lot more bigger and more powerful than the UK’s up until the industrial revolution and the about a century of everything going very badly for France. France was the most populous country in Europe by a wide margin, and back then that basically was the whole economy. It has quite a lot more land than the UK, and that land is a lot more productive too; the north of Wales and most of Scotland do not make for good farmland. Unlike Germany and Italy it united and centralised quite early, and it just outweighed Spain and the Low Countries the same way it did the UK, so for a long time France had the edge over all of its neighbours.

During the Napoleonic wars, France managed to raise forces that matched the UK, Prussia, Austria, and Spain combined in number. Some of that was due to other factors like how he organised it, but you’ve still got to have the people available somewhere if you want to match four major powers at once