There is a small difference but not much. I compared my 230V Kettle with my 400V induction stove and it’s within 5% or so. Obviously it depends a bit on what pot you use. I’m guessing most losses come from the lack of insulation on the metal pot.

Why? I'm not sure I understand the logic.

For example this: https://www.emag.ro/plita-cu-inductie-aeg-hob-hood-60-cm-ikb... (in the EU), at max power can supposedly reach 7.3kW.

Edit: Checked per element, max 3.7k, more than enough anyway.

For the induction cooktop, there's circuitry to drive the induction system, which then creates magnetic fields, which then interacts with the metal pot, which gets hot and heats the water on one side while radiating heat into the air on the other. There's a lot of stages for losses here.

On an electric kettle, there's just a heating element, often directly bathed in the hot water.

There's absolutely less losses with the electric kettle, so for a 3kW kettle and a 3kW induction cooktop the kettle is slightly more efficient. Slightly.

The contact surface of the pot is much larger, though, I'd expect. It's also not localized.

Hmm, I measured it once (temp increase over time, computed back into watts, compared to a watt meter on the induction cooker), and I found that of the 3,5kW I put in, 80% actually convert to temperature increase in the water. That is not too bad, is it? Are electric kettles more efficient?

They should make turbo kettles that hook up to 3 phase power like a stove. That seems like it would be fun. Why stop at 3kW, when you can have 11?

Now I want a kettle designed for a J1772 EV plug. Why stop at 11kW when you can have 19kW?