I consider 9 kg as light for a road bike. Mine weighs 8 kg and is by far the lightest road bike I have owned. What I do like is that I can easily lift it up and put the front wheel over the hook in my garage to keep it out of the way when not in use. I have a 11.7 kg electric road bike and that I keep in a shed in a floor rack.

On the road the main difference is that the e-bike had too great a spread with the OEM 44t chainring and 11-42t cassette (which I changed for a 11-34t one), as compared to my Trek 5200 that has 53/39 chainrings and a 12-25 cassette. Bike weight matters when accelerating and going up hills but it matters far less than the gearing of the bike.

I bought the electric road bike because where I ride I often encounter 8-15 mph headwinds and with the e-bike I can maintain the same speed as with my regular road bike with no wind. I get more aerobic conditioning and enjoy the rides more.

Going up a grade the energy expended is recovered in large part on the downhill sections but with wind this is not the case. A side wind exerts two-thirds the vector force of a head wind so 75% of the time the wind is likely to an obstacle.