You say "Our criteria for choosing a kettle were no different to anyone else's" (I've fixed the English). I think your criteria may in fact be different to other people's:
1. Kilowatts tell you how much power a kettle uses, not how efficient it is - some 3kw kettles will boil more slowly and use more energy than some lower-powered kettles. I'd agree that, in the absence of proper testing, it's a good idea to go for 3kw, but if you read Which? reviews you'll find out which kettles are most efficient.
2. Few people regularly boil more than a litre of water, so capacity will be unimportant or at the bottom of the list, for most people.
3. Others might have their own views on required finish!
4. Others might be prepared to pay more for superior performance or looks.
At the top of my list, before any of yours except perhaps appearance, would be:
1. Lid that opens easily and widely enough for water to be poured into the kettle from a mug or other measuring container.
2. Ability to boil just one cup of water.
3. Switches off when lifted from base, to eliminate the risk of unwittingly putting it back down empty but still switched on.
4. Switches off within a couple of seconds of boiling point being reached.
5. Scale filter that works well but allows decent water flow.
Others might have different priorities such as noise levels.