I've a full carbon race bike at around 9kg, my audax bike at around 11 and commute on a Edinburgh Bike cyclocross which is over 15 with the racks and lights. In addition I can have 20kg in my pannier bags. I've a very short commute, but I've never liked the bike. It's a workhorse, does what I ask, I can coax it up to a reasonable speed over 25 miles or so if I'm working away and take it with me, but I've never really rated it. In contrast my previous work bike was an Edinburgh bike branded tourer, which I did like.
The carbon bike is fast, twitchy and definitely climbs better than any of the others. The audax bike is more comfortable, has wider tyres, eats miles and has hydraulic discs and thru-axles. Both of these features have been a revelation. It would be the one I would keep if I could only have one. So for me it isn't only about weight, but a combination of comfort, features, gears, ride quality plus the fact I got an amazing deal in buying it.