First off, kudos to HT for adding a non-realistic feature that so many of us love as a usability enhancement.
Anyway, autopilots are not very smart. They are designed to seek a particular equilibrium and that's it. For autopilot climb mode, it is designed to seek a wings level particular speed (set with .speed or defaulted). The only way it knows how to do this is to adjust pitch trim. It knows that more down pitch will increase speed and more up pitch will decrease speed. That's all the smarts it has.
If you want to be as lazy as possible, you set the Auto takeoff preference. When you takeoff, it will climb for a bit at a slow speed, but will eventually start increasing speed. When it is close to the climb speed you can change to autopilot climb mode with little fuss. The moral of the story is that smarts are in the pilot, not Otto.