We haven’t looked at the F series scooters at all, but I would really like to.
My guess is that you’re exactly right though, that the difference is battery, firmware and controller, in terms of power output.
It’s interesting the way they do the ES2 vs ES4. If you take and ES2, or E22 and pop on an external battery, the scooter automatically bumps up the top speed! So in that case, they are limiting top speed to help the rider not use up the battery too quickly on the ES2 and E22 (and also, of course, helping sell the larger version).
Let us know how you like the F20. Post photos if you’ve got them :-)