I don't agree that most of the backpacking folks count what they are wearing all the time and I prefer to not count it myself.

I tend to count all gear, bags, and extra clothing that is not worn all of the time when on the bike in the base weight. I count the bike, tool wedge with tools and tubes, and empty water bottles, as part of the bike. I do track a base weight, a bike weight, and a combined weight.

I have not found my total MTB rig including the bike is heavier than the road one.